Copyright © 2005-2015 Jean-Francois Dockes
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This document introduces full text search notions and describes the installation and use of the Recoll application. This version describes Recoll 1.21.
Table of Contents
ptrans fileIf you do not like reading manuals (who does?) but wish to give Recoll a try, just install the application and start the recoll graphical user interface (GUI), which will ask permission to index your home directory by default, allowing you to search immediately after indexing completes.
Do not do this if your home directory contains a huge number of documents and you do not want to wait or are very short on disk space. In this case, you may first want to customize the configuration to restrict the indexed area (for the very impatient with a completed package install, from the recoll GUI: → , then adjust the Top directories section).
Also be aware that you may need to install the appropriate supporting applications for document types that need them (for example antiword for Microsoft Word files).
Recoll is a full text search application. Full text search finds your data by content rather than by external attributes (like a file name). You specify words (terms) which should or should not appear in the text you are looking for, and receive in return a list of matching documents, ordered so that the most relevant documents will appear first.
You do not need to remember in what file or email message you stored a given piece of information. You just ask for related terms, and the tool will return a list of documents where these terms are prominent, in a similar way to Internet search engines.
Full text search applications try to determine which documents are most relevant to the search terms you provide. Computer algorithms for determining relevance can be very complex, and in general are inferior to the power of the human mind to rapidly determine relevance. The quality of relevance guessing is probably the most important aspect when evaluating a search application.
In many cases, you are looking for all the forms of a
        word, including plurals, different tenses for a verb, or
        terms derived from the same root or stem (example: floor, floors, floored,
        flooring...). Queries are usually automatically
        expanded to all such related terms (words that reduce to
        the same stem). This can be prevented for searching for a
        specific form.
Stemming, by itself, does not accommodate for
        misspellings or phonetic searches. A full text search
        application may also support this form of approximation.
        For example, a search for aliterattion returning no
        result may propose, depending on index contents, alliteration alteration alterations
        altercation as possible replacement terms.
Recoll uses the Xapian information retrieval library as its storage and retrieval engine. Xapian is a very mature package using a sophisticated probabilistic ranking model.
The Xapian library manages an index database which describes where terms appear in your document files. It efficiently processes the complex queries which are produced by the Recoll query expansion mechanism, and is in charge of the all-important relevance computation task.
Recoll provides the mechanisms and interface to get data into and out of the index. This includes translating the many possible document formats into pure text, handling term variations (using Xapian stemmers), and spelling approximations (using the aspell speller), interpreting user queries and presenting results.
In a shorter way, Recoll does the dirty footwork, Xapian deals with the intelligent parts of the process.
The Xapian index can be big (roughly the size of the original document set), but it is not a document archive. Recoll can only display documents that still exist at the place from which they were indexed. (Actually, there is a way to reconstruct a document from the information in the index, but the result is not nice, as all formatting, punctuation and capitalization are lost).
Recoll stores all internal data in Unicode UTF-8 format, and it can index files of many types with different character sets, encodings, and languages into the same index. It can process documents embedded inside other documents (for example a pdf document stored inside a Zip archive sent as an email attachment...), down to an arbitrary depth.
Stemming is the process by which Recoll reduces words to their radicals so that searching does not depend, for example, on a word being singular or plural (floor, floors), or on a verb tense (flooring, floored). Because the mechanisms used for stemming depend on the specific grammatical rules for each language, there is a separate Xapian stemmer module for most common languages where stemming makes sense.
Recoll stores the unstemmed versions of terms in the main index and uses auxiliary databases for term expansion (one for each stemming language), which means that you can switch stemming languages between searches, or add a language without needing a full reindex.
Storing documents written in different languages in the same index is possible, and commonly done. In this situation, you can specify several stemming languages for the index.
Recoll currently makes no attempt at automatic language recognition, which means that the stemmer will sometimes be applied to terms from other languages with potentially strange results. In practise, even if this introduces possibilities of confusion, this approach has been proven quite useful, and it is much less cumbersome than separating your documents according to what language they are written in.
Before version 1.18, Recoll stripped most accents and
        diacritics from terms, and converted them to lower case
        before either storing them in the index or searching for
        them. As a consequence, it was impossible to search for a
        particular capitalization of a term (US / us), or
        to discriminate two terms based on diacritics (sake / saké, mate / maté).
As of version 1.18, Recoll can optionally store the raw terms, without accent stripping or case conversion. In this configuration, it is still possible (and most common) for a query to be insensitive to case and/or diacritics. Appropriate term expansions are performed before actually accessing the main index. This is described in more detail in the section about index case and diacritics sensitivity.
Recoll has many
        parameters which define exactly what to index, and how to
        classify and decode the source documents. These are kept in
        configuration files. A
        default configuration is copied into a standard location
        (usually something like /usr/[local/]share/recoll/examples)
        during installation. The default values set by the
        configuration files in this directory may be overridden by
        values that you set inside your personal configuration,
        found by default in the .recoll sub-directory of your home
        directory. The default configuration will index your home
        directory with default parameters and should be sufficient
        for giving Recoll a try,
        but you may want to adjust it later, which can be done
        either by editing the text files or by using configuration
        menus in the recoll GUI. Some other
        parameters affecting only the recoll GUI are stored in
        the standard location defined by Qt.
The indexing process is started automatically the first time you execute the recoll GUI. Indexing can also be performed by executing the recollindex command. Recoll indexing is multithreaded by default when appropriate hardware resources are available, and can perform in parallel multiple tasks among text extraction, segmentation and index updates.
Searches are usually performed inside the recoll GUI, which has many options to help you find what you are looking for. However, there are other ways to perform Recoll searches: mostly a command line interface, a Python programming interface, a KDE KIO slave module, and Ubuntu Unity Lens (for older versions) or Scope (for current versions) modules.
Indexing is the process by which the set of documents is
        analyzed and the data entered into the database.
        Recoll indexing is
        normally incremental: documents will only be processed if
        they have been modified since the last run. On the first
        execution, all documents will need processing. A full index
        build can be forced later by specifying an option to the
        indexing command (recollindex -z or -Z).
recollindex skips files
        which caused an error during a previous pass. This is a
        performance optimization, and a new behaviour in version
        1.21 (failed files were always retried by previous
        versions). The command line option -k can be set to retry failed files, for
        example after updating a filter.
The following sections give an overview of different aspects of the indexing processes and configuration, with links to detailed sections.
Depending on your data, temporary files may be needed
        during indexing, some of them possibly quite big. You can
        use the RECOLL_TMPDIR or
        TMPDIR environment variables to
        determine where they are created (the default is to use
        /tmp). Using TMPDIR has the nice property that it may
        also be taken into account by auxiliary commands executed
        by recollindex.
Recoll indexing can be performed along two different modes:
Periodic (or batch) indexing: indexing takes place at discrete times, by executing the recollindex command. The typical usage is to have a nightly indexing run programmed into your cron file.
Real time indexing: indexing takes place as soon as a file is created or changed. recollindex runs as a daemon and uses a file system alteration monitor such as inotify, Fam or Gamin to detect file changes.
The choice between the two methods is mostly a matter of preference, and they can be combined by setting up multiple indexes (ie: use periodic indexing on a big documentation directory, and real time indexing on a small home directory). Monitoring a big file system tree can consume significant system resources.
The choice of method and the parameters used can be configured from the recoll GUI: →
The parameters describing what is to be indexed and local preferences are defined in text files contained in a configuration directory.
All parameters have defaults, defined in system-wide files.
Without further configuration, Recoll will index all appropriate files from your home directory, with a reasonable set of defaults.
A default personal configuration directory
          ($HOME/.recoll/) is created
          when a Recoll program is
          first executed. It is possible to create other
          configuration directories, and use them by setting the
          RECOLL_CONFDIR environment
          variable, or giving the -c
          option to any of the Recoll commands.
In some cases, it may be interesting to index different areas of the file system to separate databases. You can do this by using multiple configuration directories, each indexing a file system area to a specific database. Typically, this would be done to separate personal and shared indexes, or to take advantage of the organization of your data to improve search precision.
The generated indexes can be queried concurrently in a transparent manner.
For index generation, multiple configurations are totally independant from each other. When multiple indexes need to be used for a single search, some parameters should be consistent among the configurations.
Recoll knows about quite a few different document types. The parameters for document types recognition and processing are set in configuration files.
Most file types, like HTML or word processing files, only hold one document. Some file types, like email folders or zip archives, can hold many individually indexed documents, which may themselves be compound ones. Such hierarchies can go quite deep, and Recoll can process, for example, a LibreOffice document stored as an attachment to an email message inside an email folder archived in a zip file...
Recoll indexing processes plain text, HTML, OpenDocument (Open/LibreOffice), email formats, and a few others internally.
Other file types (ie: postscript, pdf, ms-word, rtf
          ...) need external applications for preprocessing. The
          list is in the installation section.
          After every indexing operation, Recoll updates a list of commands
          that would be needed for indexing existing files types.
          This list can be displayed by selecting the menu option
           →  in the
          recoll GUI.
          It is stored in the missing
          text file inside the configuration directory.
By default, Recoll will try to index any file type that it has a way to read. This is sometimes not desirable, and there are ways to either exclude some types, or on the contrary to define a positive list of types to be indexed. In the latter case, any type not in the list will be ignored.
Excluding types can be done by adding wildcard name
          patterns to the skippedNames
          list, which can be done from the GUI Index configuration
          menu. For versions 1.20 and later, you can alternatively
          set the excludedmimetypes
          list in the configuration file. This can be redefined for
          subdirectories.
You can also define an exclusive list of MIME types to
          be indexed (no others will be indexed), by settting the
          indexedmimetypes
          configuration variable. Example:
indexedmimetypes = text/html application/pdf
          
          It is possible to redefine this parameter for subdirectories. Example:
[/path/to/my/dir]
indexedmimetypes = application/pdf
          
          (When using sections like this, don't forget that they remain in effect until the end of the file or another section indicator).
excludedmimetypes or
          indexedmimetypes, can be set
          either by editing the main
          configuration file (recoll.conf), or from the GUI index
          configuration tool.
Indexing may fail for some documents, for a number of reasons: a helper program may be missing, the document may be corrupt, we may fail to uncompress a file because no file system space is available, etc.
Recoll versions prior to 1.21 always retried to index files which had previously caused an error. This guaranteed that anything that may have become indexable (for example because a helper had been installed) would be indexed. However this was bad for performance because some indexing failures may be quite costly (for example failing to uncompress a big file because of insufficient disk space).
The indexer in Recoll
          versions 1.21 and later do not retry failed file by
          default. Retrying will only occur if an explicit option
          (-k) is set on the
          recollindex
          command line, or if a script executed when recollindex starts up
          says so. The script is defined by a configuration
          variable (checkneedretryindexscript), and makes a
          rather lame attempt at deciding if a helper command may
          have been installed, by checking if any of the common
          bin directories have
          changed.
In the rare case where the index becomes corrupted
          (which can signal itself by weird search results or
          crashes), the index files need to be erased before
          restarting a clean indexing pass. Just delete the
          xapiandb directory (see
          next section), or,
          alternatively, start the next recollindex with the
          -z option, which will reset
          the database before indexing.
The default location for the index data is the
        xapiandb subdirectory of the
        Recoll configuration
        directory, typically $HOME/.recoll/xapiandb/. This can be
        changed via two different methods (with different
        purposes):
You can specify a different configuration
              directory by setting the RECOLL_CONFDIR environment variable,
              or using the -c option to
              the Recoll commands.
              This method would typically be used to index
              different areas of the file system to different
              indexes. For example, if you were to issue the
              following commands:
export RECOLL_CONFDIR=~/.indexes-email
recoll
          
              Then Recoll would
              use configuration files stored in ~/.indexes-email/ and, (unless
              specified otherwise in recoll.conf) would look for the
              index in ~/.indexes-email/xapiandb/.
Using multiple configuration directories and configuration options allows you to tailor multiple configurations and indexes to handle whatever subset of the available data you wish to make searchable.
For a given configuration directory, you can
              specify a non-default storage location for the index
              by setting the dbdir
              parameter in the configuration file (see the
              
              configuration section). This method would mainly
              be of use if you wanted to keep the configuration
              directory in its default location, but desired
              another location for the index, typically out of disk
              occupation concerns.
The size of the index is determined by the size of the set of documents, but the ratio can vary a lot. For a typical mixed set of documents, the index size will often be close to the data set size. In specific cases (a set of compressed mbox files for example), the index can become much bigger than the documents. It may also be much smaller if the documents contain a lot of images or other non-indexed data (an extreme example being a set of mp3 files where only the tags would be indexed).
Of course, images, sound and video do not increase the index size, which means that nowadays (2012), typically, even a big index will be negligible against the total amount of data on the computer.
The index data directory (xapiandb) only contains data that can be
        completely rebuilt by an index run (as long as the original
        documents exist), and it can always be destroyed
        safely.
Xapian versions usually support several formats for index storage. A given major Xapian version will have a current format, used to create new indexes, and will also support the format from the previous major version.
Xapian will not convert automatically an existing index from the older format to the newer one. If you want to upgrade to the new format, or if a very old index needs to be converted because its format is not supported any more, you will have to explicitly delete the old index, then run a normal indexing process.
Using the -z option to
          recollindex
          is not sufficient to change the format, you will have to
          delete all files inside the index directory (typically
          ~/.recoll/xapiandb) before
          starting the indexing.
The Recoll index does not hold copies of the indexed documents. But it does hold enough data to allow for an almost complete reconstruction. If confidential data is indexed, access to the database directory should be restricted.
Recoll (since version 1.4) will create the configuration directory with a mode of 0700 (access by owner only). As the index data directory is by default a sub-directory of the configuration directory, this should result in appropriate protection.
If you use another setup, you should think of the kind
          of protection you need for your index, set the directory
          and files access modes appropriately, and also maybe
          adjust the umask used during
          index updates.
Variables set inside the Recoll configuration files control which areas of the file system are indexed, and how files are processed. These variables can be set either by editing the text files or by using the dialogs in the recoll GUI.
The first time you start recoll, you will be asked
        whether or not you would like it to build the index. If you
        want to adjust the configuration before indexing, just
        click Cancel at this point,
        which will get you into the configuration interface. If you
        exit at this point, recoll
        will have created a ~/.recoll
        directory containing empty configuration files, which you
        can edit by hand.
The configuration is documented inside the installation chapter
        of this document, or in the recoll.conf(5) man page, but
        the most current information will most likely be the
        comments inside the sample file. The most immediately
        useful variable you may interested in is probably topdirs, which determines what
        subtrees get indexed.
The applications needed to index file types other than text, HTML or email (ie: pdf, postscript, ms-word...) are described in the external packages section.
As of Recoll 1.18 there are two incompatible types of Recoll indexes, depending on the treatment of character case and diacritics. The next section describes the two types in more detail.
Multiple Recoll
          indexes can be created by using several configuration
          directories which are usually set to index different
          areas of the file system. A specific index can be
          selected for updating or searching, using the
          RECOLL_CONFDIR environment
          variable or the -c option to
          recoll and
          recollindex.
A typical usage scenario for the multiple index feature would be for a system administrator to set up a central index for shared data, that you choose to search or not in addition to your personal data. Of course, there are other possibilities. There are many cases where you know the subset of files that should be searched, and where narrowing the search can improve the results. You can achieve approximately the same effect with the directory filter in advanced search, but multiple indexes will have much better performance and may be worth the trouble.
A recollindex program instance can only update one specific index.
The main index (defined by RECOLL_CONFDIR or -c) is always active. If this is
          undesirable, you can set up your base configuration to
          index an empty directory.
The different search interfaces (GUI, command line, ...) have different methods to define the set of indexes to be used, see the appropriate section.
If a set of multiple indexes are to be used together for searches, some configuration parameters must be consistent among the set. These are parameters which need to be the same when indexing and searching. As the parameters come from the main configuration when searching, they need to be compatible with what was set when creating the other indexes (which came from their respective configuration directories).
Most importantly, all indexes to be queried concurrently must have the same option concerning character case and diacritics stripping, but there are other constraints. Most of the relevant parameters are described in the linked section.
As of Recoll version
          1.18 you have a choice of building an index with terms
          stripped of character case and diacritics, or one with
          raw terms. For a source term of Résumé, the former will
          store resume, the latter
          Résumé.
Each type of index allows performing searches insensitive to case and diacritics: with a raw index, the user entry will be expanded to match all case and diacritics variations present in the index. With a stripped index, the search term will be stripped before searching.
A raw index allows for another possibility which a
          stripped index cannot offer: using case and diacritics to
          discriminate between terms, returning different results
          when searching for US and
          us or resume and résumé. Read the section
          about search case and diacritics sensitivity for more
          details.
The type of index to be created is controlled by the
          indexStripChars
          configuration variable which can only be changed by
          editing the configuration file. Any change implies an
          index reset (not automated by Recoll), and all indexes in a search
          must be set in the same way (again, not checked by
          Recoll).
If the indexStripChars is
          not set, Recoll 1.18
          creates a stripped index by default, for compatibility
          with previous versions.
As a cost for added capability, a raw index will be slightly bigger than a stripped one (around 10%). Also, searches will be more complex, so probably slightly slower, and the feature is still young, so that a certain amount of weirdness cannot be excluded.
One of the most adverse consequence of using a raw index is that some phrase and proximity searches may become impossible: because each term needs to be expanded, and all combinations searched for, the multiplicative expansion may become unmanageable.
Most parameters for a given index configuration can be
          set from a recoll GUI running on
          this configuration (either as default, or by setting
          RECOLL_CONFDIR or the
          -c option.)
The interface is started from the → menu entry. It is divided in four tabs, Global parameters, Local parameters, Web history (which is explained in the next section) and Search parameters.
The Global parameters tab allows setting global variables, like the lists of top directories, skipped paths, or stemming languages.
The Local parameters tab allows setting variables that can be redefined for subdirectories. This second tab has an initially empty list of customisation directories, to which you can add. The variables are then set for the currently selected directory (or at the top level if the empty line is selected).
The Search parameters section defines parameters which are used at query time, but are global to an index and affect all search tools, not only the GUI.
The meaning for most entries in the interface is
          self-evident and documented by a ToolTip popup on the text label. For
          more detail, you will need to refer to the configuration
          section of this guide.
The configuration tool normally respects the comments and most of the formatting inside the configuration file, so that it is quite possible to use it on hand-edited files, which you might nevertheless want to backup first...
With the help of a Firefox extension, Recoll can index the Internet pages that you visit. The extension was initially designed for the Beagle indexer, but it has recently be renamed and better adapted to Recoll.
The extension works by copying visited WEB pages to an indexing queue directory, which Recoll then processes, indexing the data, storing it into a local cache, then removing the file from the queue.
This feature can be enabled in the GUI Index configuration panel, or by editing
        the configuration file (set processwebqueue to 1).
A current pointer to the extension can be found, along with up-to-date instructions, on the Recoll wiki.
A copy of the indexed WEB pages is retained by Recoll in a local cache (from which previews can be fetched). The cache size can be adjusted from the Index configuration / Web history panel. Once the maximum size is reached, old pages are purged - both from the cache and the index - to make room for new ones, so you need to explicitly archive in some other place the pages that you want to keep indefinitely.
User extended attributes are named pieces of information that most modern file systems can attach to any file.
Recoll versions 1.19 and later process extended attributes as document fields by default. For older versions, this has to be activated at build time.
A freedesktop standard defines a few special attributes, which are handled as such by Recoll:
If set, this overrides any other determination of the file MIME type.
By default, other attributes are handled as Recoll fields. On Linux, the
        user prefix is removed from
        the name. This can be configured more precisely inside the
        fields configuration file.
During indexing, it is possible to import metadata for each file by executing commands. For example, this could extract user tag data for the file and store it in a field for indexing.
See the section about
        the metadatacmds field in
        the main configuration chapter for more detail.
Indexing is always performed by the recollindex program,
          which can be started either from the command line or from
          the  menu in the
          recoll GUI
          program. When started from the GUI, the indexing will run
          on the same configuration recoll was started on.
          When started from the command line, recollindex will use
          the RECOLL_CONFDIR variable or
          accept a -c confdir option to specify
          a non-default configuration directory.
If the recoll program finds no index when it starts, it will automatically start indexing (except if canceled).
The recollindex indexing process can be interrupted by sending an interrupt (Ctrl-C, SIGINT) or terminate (SIGTERM) signal. Some time may elapse before the process exits, because it needs to properly flush and close the index. This can also be done from the recoll GUI → menu entry.
After such an interruption, the index will be somewhat inconsistent because some operations which are normally performed at the end of the indexing pass will have been skipped (for example, the stemming and spelling databases will be inexistant or out of date). You just need to restart indexing at a later time to restore consistency. The indexing will restart at the interruption point (the full file tree will be traversed, but files that were indexed up to the interruption and for which the index is still up to date will not need to be reindexed).
recollindex has a number of other options which are described in its man page. Only a few will be described here.
Option -z will reset the
          index when starting. This is almost the same as
          destroying the index files (the nuance is that the
          Xapian format version
          will not be changed).
Option -Z will force the
          update of all documents without resetting the index
          first. This will not have the "clean start" aspect of
          -z, but the advantage is that
          the index will remain available for querying while it is
          rebuilt, which can be a significant advantage if it is
          very big (some installations need days for a full index
          rebuild).
Option -k will force
          retrying files which previously failed to be indexed, for
          example because of a missing helper program.
Of special interest also, maybe, are the -i and -f
          options. -i allows indexing
          an explicit list of files (given as command line
          parameters or read on stdin). -f
          tells recollindex to ignore
          file selection parameters from the configuration.
          Together, these options allow building a custom file
          selection process for some area of the file system, by
          adding the top directory to the skippedPaths list and using an
          appropriate file selection method to build the file list
          to be fed to recollindex
          -if. Trivial example:
            find . -name indexable.txt -print | recollindex -if
          
          recollindex
          -i will not descend into
          subdirectories specified as parameters, but just add them
          as index entries. It is up to the external file selection
          method to build the complete file list.
The most common way to set up indexing is to have a
          cron task execute it every night. For example the
          following crontab entry
          would do it every day at 3:30AM (supposing recollindex is in your
          PATH):
30 3 * * * recollindex > /some/tmp/dir/recolltrace 2>&1
Or, using anacron:
1 15 su mylogin -c "recollindex recollindex > /tmp/rcltraceme 2>&1"
As of version 1.17 the Recoll GUI has dialogs to manage
          crontab entries for
          recollindex. You can
          reach them from the  →  menu. They only
          work with the good old cron, and do not give
          access to all features of cron scheduling.
The usual command to edit your crontab is crontab -e (which will usually start the
          vi editor
          to edit the file). You may have more sophisticated tools
          available on your system.
Please be aware that there may be differences between your usual interactive command line environment and the one seen by crontab commands. Especially the PATH variable may be of concern. Please check the crontab manual pages about possible issues.
Real time monitoring/indexing is performed by starting
        the recollindex -m command. With this option, recollindex will detach
        from the terminal and become a daemon, permanently
        monitoring file changes and updating the index.
Under KDE, Gnome and some other desktop
        environments, the daemon can automatically started when you
        log in, by creating a desktop file inside the ~/.config/autostart directory. This can
        be done for you by the Recoll GUI. Use the 
        menu.
With older X11 setups, starting the daemon is normally performed as part of the user session script.
The rclmon.sh script can
        be used to easily start and stop the daemon. It can be
        found in the examples
        directory (typically /usr/local/[share/]recoll/examples).
For example, my out of fashion xdm-based session has a .xsession script with the following lines
        at the end:
recollconf=$HOME/.recoll-home recolldata=/usr/local/share/recoll RECOLL_CONFDIR=$recollconf $recolldata/examples/rclmon.sh start fvwm
The indexing daemon gets started, then the window manager, for which the session waits.
By default the indexing daemon will monitor the state of
        the X11 session, and exit when it finishes, it is not
        necessary to kill it explicitly. (The X11 server monitoring can be disabled
        with option -x to recollindex).
If you use the daemon completely out of an X11 session, you need to add option
        -x to disable X11 session monitoring (else the
        daemon will not start).
By default, the messages from the indexing daemon will
        be setn to the same file as those from the interactive
        commands (logfilename). You
        may want to change this by setting the daemlogfilename and daemloglevel configuration parameters.
        Also the log file will only be truncated when the daemon
        starts. If the daemon runs permanently, the log file may
        grow quite big, depending on the log level.
When building Recoll,
        the real time indexing support can be customised during
        package configuration with the
        --with[out]-fam or --with[out]-inotify options. The default is
        currently to include inotify monitoring on systems that
        support it, and, as of Recoll 1.17, gamin support on FreeBSD.
While it is convenient that data is indexed in real time, repeated indexing can generate a significant load on the system when files such as email folders change. Also, monitoring large file trees by itself significantly taxes system resources. You probably do not want to enable it if your system is short on resources. Periodic indexing is adequate in most cases.
On Linux systems, monitoring a big tree may need
          increasing the resources available to inotify, which are
          normally defined in /etc/sysctl.conf.
### inotify
#
# cat  /proc/sys/fs/inotify/max_queued_events   - 16384
# cat  /proc/sys/fs/inotify/max_user_instances  - 128
# cat  /proc/sys/fs/inotify/max_user_watches    - 16384
#
# -- Change to:
#
fs.inotify.max_queued_events=32768
fs.notify.max_user_instances=256
fs.inotify.max_user_watches=32768
          
          Especially, you will need to trim your tree or adjust
          the max_user_watches value
          if indexing exits with a message about errno ENOSPC (28) from inotify_add_watch.
When using the real time monitor, it may happen that some files need to be indexed, but change so often that they impose an excessive load for the system.
Recoll provides a
          configuration option to specify the minimum time before
          which a file, specified by a wildcard pattern, cannot be
          reindexed. See the mondelaypatterns parameter in the
          configuration
          section.
The recoll program provides the main user interface for searching. It is based on the Qt library.
recoll has two search modes:
Simple search (the default, on the main screen) has a single entry field where you can enter multiple words.
Advanced search (a panel accessed through the Tools menu or the toolbox bar icon) has multiple entry fields, which you may use to build a logical condition, with additional filtering on file type, location in the file system, modification date, and size.
In most cases, you can enter the terms as you think them, even if they contain embedded punctuation or other non-textual characters. For example, Recoll can handle things like email addresses, or arbitrary cut and paste from another text window, punctation and all.
The main case where you should enter text differently from how it is printed is for east-asian languages (Chinese, Japanese, Korean). Words composed of single or multiple characters should be entered separated by white space in this case (they would typically be printed without white space).
Some searches can be quite complex, and you may want to re-use them later, perhaps with some tweaking. Recoll versions 1.21 and later can save and restore searches, using XML files. See Saving and restoring queries.
Start the recoll program.
Possibly choose a search mode: Any term, All terms, File name or Query language.
Enter search term(s) in the text field at the top of the window.
Click the Search button or hit the Enter key to start the search.
The initial default search mode is Query language. Without special directives, this will look for documents containing all of the search terms (the ones with more terms will get better scores), just like the All terms mode which will ignore such directives. Any term will search for documents where at least one of the terms appear.
The Query Language features are described in a separate section.
All search modes allow wildcards inside terms
          (*, ?, []). You
          may want to have a look at the section about
          wildcards for more information about this.
File name will specifically look for file names. The point of having a separate file name search is that wild card expansion can be performed more efficiently on a small subset of the index (allowing wild cards on the left of terms without excessive penality). Things to know:
White space in the entry should match white space in the file name, and is not treated specially.
The search is insensitive to character case and accents, independantly of the type of index.
An entry without any wild card character and not
                capitalized will be prepended and appended with '*'
                (ie: etc
                -> *etc*, but
                Etc ->
                etc).
If you have a big index (many files), excessively generic fragments may result in inefficient searches.
You can search for exact phrases (adjacent words in a
          given order) by enclosing the input inside double quotes.
          Ex: "virtual reality".
When using a stripped index, character case has no
          influence on search, except that you can disable stem
          expansion for any term by capitalizing it. Ie: a search
          for floor will also normally
          look for flooring,
          floored, etc., but a search
          for Floor will only look for
          floor, in any character
          case. Stemming can also be disabled globally in the
          preferences. When using a raw index, the
          rules are a bit more complicated.
Recoll remembers the last few searches that you performed. You can use the simple search text entry widget (a combobox) to recall them (click on the thing at the right of the text field). Please note, however, that only the search texts are remembered, not the mode (all/any/file name).
Typing Esc Space while entering a word in the simple search entry will open a window with possible completions for the word. The completions are extracted from the database.
Double-clicking on a word in the result list or a preview window will insert it into the simple search entry field.
You can cut and paste any text into an All terms or Any
          term search field, punctuation, newlines and all -
          except for wildcard characters (single ? characters are ok). Recoll will process it and produce a
          meaningful search. This is what most differentiates this
          mode from the Query
          Language mode, where you have to care about the
          syntax.
You can use the → dialog for more complex searches.
After starting a search, a list of results will instantly be displayed in the main list window.
By default, the document list is presented in order of relevance (how well the system estimates that the document matches the query). You can sort the result by ascending or descending date by using the vertical arrows in the toolbar.
Clicking on the Preview
          link for an entry will open an internal preview window
          for the document. Further Preview clicks for the same search will
          open tabs in the existing preview window. You can use
          Shift+Click
          to force the creation of another preview window, which
          may be useful to view the documents side by side. (You
          can also browse successive results in a single preview
          window by typing Shift+ArrowUp/Down in the
          window).
Clicking the Open link
          will start an external viewer for the document. By
          default, Recoll lets the
          desktop choose the appropriate application for most
          document types (there is a short list of exceptions, see
          further). If you prefer to completely customize the
          choice of applications, you can uncheck the Use desktop preferences option in the
          GUI preferences dialog, and click the Choose editor applications button to
          adjust the predefined Recoll choices. The tool accepts
          multiple selections of MIME types (e.g. to set up the
          editor for the dozens of office file types).
Even when Use desktop preferences is checked, there is a small list of exceptions, for MIME types where the Recoll choice should override the desktop one. These are applications which are well integrated with Recoll, especially evince for viewing PDF and Postscript files because of its support for opening the document at a specific page and passing a search string as an argument. Of course, you can edit the list (in the GUI preferences) if you would prefer to lose the functionality and use the standard desktop tool.
You may also change the choice of applications by
          editing the mimeview configuration file if you
          find this more convenient.
Each result entry also has a right-click menu with an Open With entry. This lets you choose an application from the list of those which registered with the desktop for the document MIME type.
The Preview and
          Open edit links may not be
          present for all entries, meaning that Recoll has no configured way to
          preview a given file type (which was indexed by name
          only), or no configured external editor for the file
          type. This can sometimes be adjusted simply by tweaking
          the mimemap and mimeview configuration files (the
          latter can be modified with the user preferences
          dialog).
The format of the result list entries is entirely configurable by using the preference dialog to edit an HTML fragment.
You can click on the Query
          details link at the top of the results page to see
          the query actually performed, after stem expansion and
          other processing.
Double-clicking on any word inside the result list or a preview window will insert it into the simple search text.
The result list is divided into pages (the size of which you can change in the preferences). Use the arrow buttons in the toolbar or the links at the bottom of the page to browse the results.
When a search yields no result, and if the aspell dictionary is configured, Recoll will try to check for misspellings among the query terms, and will propose lists of replacements. Clicking on one of the suggestions will replace the word and restart the search. You can hold any of the modifier keys (Ctrl, Shift, etc.) while clicking if you would rather stay on the suggestion screen because several terms need replacement.
Apart from the preview and edit links, you can display a pop-up menu by right-clicking over a paragraph in the result list. This menu has the following entries:
Preview
Open
Open With
Run Script
Copy File Name
Copy Url
Save to File
Find similar
Preview Parent document
Open Parent document
Open Snippets Window
The Preview and Open entries do the same thing as the corresponding links.
Open With lets you
            open the document with one of the applications claiming
            to be able to handle its MIME type (the information
            comes from the .desktop
            files in /usr/share/applications).
Run Script allows starting an arbitrary command on the result file. It will only appear for results which are top-level files. See further for a more detailed description.
The Copy File Name and Copy Url copy the relevant data to the clipboard, for later pasting.
Save to File allows saving the contents of a result document to a chosen file. This entry will only appear if the document does not correspond to an existing file, but is a subdocument inside such a file (ie: an email attachment). It is especially useful to extract attachments with no associated editor.
The Open/Preview Parent document entries allow working with the higher level document (e.g. the email message an attachment comes from). Recoll is sometimes not totally accurate as to what it can or can't do in this area. For example the Parent entry will also appear for an email which is part of an mbox folder file, but you can't actually visualize the mbox (there will be an error dialog if you try).
If the document is a top-level file, Open Parent will start the default file manager on the enclosing filesystem directory.
The Find similar entry will select a number of relevant term from the current document and enter them into the simple search field. You can then start a simple search, with a good chance of finding documents related to the current result. I can't remember a single instance where this function was actually useful to me...
The Open Snippets Window entry will only appear for documents which support page breaks (typically PDF, Postscript, DVI). The snippets window lists extracts from the document, taken around search terms occurrences, along with the corresponding page number, as links which can be used to start the native viewer on the appropriate page. If the viewer supports it, its search function will also be primed with one of the search terms.
In Recoll 1.15 and newer, the results can be displayed in spreadsheet-like fashion. You can switch to this presentation by clicking the table-like icon in the toolbar (this is a toggle, click again to restore the list).
Clicking on the column headers will allow sorting by the values in the column. You can click again to invert the order, and use the header right-click menu to reset sorting to the default relevance order (you can also use the sort-by-date arrows to do this).
Both the list and the table display the same underlying results. The sort order set from the table is still active if you switch back to the list mode. You can click twice on a date sort arrow to reset it from there.
The header right-click menu allows adding or deleting columns. The columns can be resized, and their order can be changed (by dragging). All the changes are recorded when you quit recoll
Hovering over a table row will update the detail area at the bottom of the window with the corresponding values. You can click the row to freeze the display. The bottom area is equivalent to a result list paragraph, with links for starting a preview or a native application, and an equivalent right-click menu. Typing Esc (the Escape key) will unfreeze the display.
Apart from the Open and Open With operations, which allow starting an application on a result document (or a temporary copy), based on its MIME type, it is also possible to run arbitrary commands on results which are top-level files, using the Run Script entry in the results pop-up menu.
The commands which will appear in the Run Script submenu must be defined by
          .desktop files inside the
          scripts subdirectory of the
          current configuration directory.
Here follows an example of a .desktop file, which could be named for
          example, ~/.recoll/scripts/myscript.desktop (the
          exact file name inside the directory is irrelevant):
[Desktop Entry]
Type=Application
Name=MyFirstScript
Exec=/home/me/bin/tryscript %F
MimeType=*/*
      
          The Name attribute
          defines the label which will appear inside the
          Run Script menu. The
          Exec attribute defines the
          program to be run, which does not need to actually be a
          script, of course. The MimeType attribute is not used, but
          needs to exist.
The commands defined this way can also be used from links inside the result paragraph.
As an example, it might make sense to write a script which would move the document to the trash and purge it from the Recoll index.
The default format for the result list entries and the detail area of the result table display an icon for each result document. The icon is either a generic one determined from the MIME type, or a thumbnail of the document appearance. Thumbnails are only displayed if found in the standard freedesktop location, where they would typically have been created by a file manager.
Recoll has no capability to create thumbnails. A relatively simple trick is to use the Open parent document/folder entry in the result list popup menu. This should open a file manager window on the containing directory, which should in turn create the thumbnails (depending on your settings). Restarting the search should then display the thumbnails.
There are also some pointers about thumbnail generation on the Recoll wiki.
The preview window opens when you first click a
          Preview link inside the
          result list.
Subsequent preview requests for a given search open new tabs in the existing window (except if you hold the Shift key while clicking which will open a new window for side by side viewing).
Starting another search and requesting a preview will create a new preview window. The old one stays open until you close it.
You can close a preview tab by typing Ctrl-W (Ctrl + W) in the window. Closing the last tab for a window will also close the window.
Of course you can also close a preview window by using the window manager button in the top of the frame.
You can display successive or previous documents from the result list inside a preview tab by typing Shift+Down or Shift+Up (Down and Up are the arrow keys).
A right-click menu in the text area allows switching between displaying the main text or the contents of fields associated to the document (ie: author, abtract, etc.). This is especially useful in cases where the term match did not occur in the main text but in one of the fields. In the case of images, you can switch between three displays: the image itself, the image metadata as extracted by exiftool and the fields, which is the metadata stored in the index.
You can print the current preview window contents by typing Ctrl-P (Ctrl + P) in the window text.
The preview window has an internal search capability, mostly controlled by the panel at the bottom of the window, which works in two modes: as a classical editor incremental search, where we look for the text entered in the entry zone, or as a way to walk the matches between the document and the Recoll query that found it.
The preview tabs have an internal incremental search function. You initiate the search either by typing a / (slash) or CTL-F inside the text area or by clicking into the Search for: text field and entering the search string. You can then use the Next and Previous buttons to find the next/previous occurrence. You can also type F3 inside the text area to get to the next occurrence.
If you have a search string entered and you use Ctrl-Up/Ctrl-Down to browse the results, the search is initiated for each successive document. If the string is found, the cursor will be positioned at the first occurrence of the search string.
If the entry area is empty when you click the Next or Previous buttons, the editor will be scrolled to show the next match to any search term (the next highlighted zone). If you select a search group from the dropdown list and click Next or Previous, the match list for this group will be walked. This is not the same as a text search, because the occurences will include non-exact matches (as caused by stemming or wildcards). The search will revert to the text mode as soon as you edit the entry area.
Selecting the → menu entry will open a window with radio- and check-buttons which can be used to activate query language fragments for filtering the current query. This can be useful if you have frequent reusable selectors, for example, filtering on alternate directories, or searching just one category of files, not covered by the standard category selectors.
The contents of the window are entirely customizable,
          and defined by the contents of the fragbuts.xml file inside the
          configuration directory. The sample file distributed with
          Recoll (which you should
          be able to find under /usr/share/recoll/examples/fragbuts.xml),
          contains an example which filters the results from the
          WEB history.
Here follows an example:
<?xml version="1.0" encoding="UTF-8"?>
<fragbuts version="1.0">
  <radiobuttons>
    <fragbut>
      <label>Include Web Results</label>
      <frag></frag>
    </fragbut>
    <fragbut>
      <label>Exclude Web Results</label>
      <frag>-rclbes:BGL</frag>
    </fragbut>
    <fragbut>
      <label>Only Web Results</label>
      <frag>rclbes:BGL</frag>
    </fragbut>
  </radiobuttons>
  <buttons>
    <fragbut>
      <label>Year 2010</label>
      <frag>date:2010-01-01/2010-12-31</frag>
    </fragbut>
    <fragbut>
      <label>My Great Directory Only</label>
      <frag>dir:/my/great/directory</frag>
    </fragbut>
  </buttons>
</fragbuts>
          Each radiobuttons or
          buttons section defines a
          line of checkbuttons or radiobuttons inside the window.
          Any number of buttons can be selected, but the
          radiobuttons in a line are exclusive.
Each fragbut section
          defines the label for a button, and the Query Language
          fragment which will be added (as an AND filter) before
          performing the query if the button is active.
This feature is new in Recoll 1.20, and will probably be refined depending on user feedback.
The advanced search dialog helps you build more complex queries without memorizing the search language constructs. It can be opened through the Tools menu or through the main toolbar.
Recoll keeps a history of searches. See Advanced search history.
The dialog has two tabs:
The first tab lets you specify terms to search for, and permits specifying multiple clauses which are combined to build the search.
The second tab lets filter the results according to file size, date of modification, MIME type, or location.
Click on the Start Search button in the advanced search dialog, or type Enter in any text field to start the search. The button in the main window always performs a simple search.
Click on the Show query
          details link at the top of the result page to see
          the query expansion.
This part of the dialog lets you constructc a query by combining multiple clauses of different types. Each entry field is configurable for the following modes:
All terms.
Any term.
None of the terms.
Phrase (exact terms in order within an adjustable window).
Proximity (terms in any order within an adjustable window).
Filename search.
Additional entry fields can be created by clicking the Add clause button.
When searching, the non-empty clauses will be combined either with an AND or an OR conjunction, depending on the choice made on the left (All clauses or Any clause).
Entries of all types except "Phrase" and "Near" accept a mix of single words and phrases enclosed in double quotes. Stemming and wildcard expansion will be performed as for simple search.
Phrases
            and Proximity searches. These two clauses work
            in similar ways, with the difference that proximity
            searches do not impose an order on the words. In both
            cases, an adjustable number (slack) of non-matched
            words may be accepted between the searched ones (use
            the counter on the left to adjust this count). For
            phrases, the default count is zero (exact match). For
            proximity it is ten (meaning that two search terms,
            would be matched if found within a window of twelve
            words). Examples: a phrase search for quick fox with a slack of 0 will match
            quick fox but not
            quick brown fox. With a
            slack of 1 it will match the latter, but not
            fox quick. A proximity
            search for quick fox with
            the default slack will match the latter, and also
            a fox is a cunning and quick
            animal.
This part of the dialog has several sections which allow filtering the results of a search according to a number of criteria
The first section allows filtering by dates of last modification. You can specify both a minimum and a maximum date. The initial values are set according to the oldest and newest documents found in the index.
The next section allows filtering the results
                  by file size. There are two entries for minimum
                  and maximum size. Enter decimal numbers. You can
                  use suffix multipliers: k/K, m/M, g/G, t/T for 1E3, 1E6, 1E9, 1E12
                  respectively.
The next section allows filtering the results by their MIME types, or MIME categories (ie: media/text/message/etc.).
You can transfer the types between two boxes, to define which will be included or excluded by the search.
The state of the file type selection can be saved as the default (the file type filter will not be activated at program start-up, but the lists will be in the restored state).
The bottom section allows restricting the search results to a sub-tree of the indexed area. You can use the Invert checkbox to search for files not in the sub-tree instead. If you use directory filtering often and on big subsets of the file system, you may think of setting up multiple indexes instead, as the performance may be better.
You can use relative/partial paths for
                  filtering. Ie, entering dirA/dirB would match either
                  /dir1/dirA/dirB/myfile1 or
                  /dir2/dirA/dirB/someother/myfile2.
The advanced search tool memorizes the last 100 searches performed. You can walk the saved searches by using the up and down arrow keys while the keyboard focus belongs to the advanced search dialog.
The complex search history can be erased, along with the one for simple search, by selecting the → menu entry.
Recoll automatically manages the expansion of search terms to their derivatives (ie: plural/singular, verb inflections). But there are other cases where the exact search term is not known. For example, you may not remember the exact spelling, or only know the beginning of the name.
The search will only propose replacement terms with spelling variations when no matching document were found. In some cases, both proper spellings and mispellings are present in the index, and it may be interesting to look for them explicitely.
The term explorer tool (started from the toolbar icon or from the Term explorer entry of the Tools menu) can be used to search the full index terms list. It has three modes of operations:
In this mode of operation, you can enter a
                search string with shell-like wildcards (*, ?, []).
                ie: xapi*
                would display all index terms beginning with
                xapi.
                (More about wildcards here).
This mode will accept a regular expression as
                input. Example: word[0-9]+. The
                expression is implicitely anchored at the
                beginning. Ie: press will match
                pression
                but not expression. You can
                use .*press to match
                the latter, but be aware that this will cause a
                full index term list scan, which can be quite
                long.
This mode will perform the usual stem expansion normally done as part user input processing. As such it is probably mostly useful to demonstrate the process.
In this mode, you enter the term as you think it is spelled, and Recoll will do its best to find index terms that sound like your entry. This mode uses the Aspell spelling application, which must be installed on your system for things to work (if your documents contain non-ascii characters, Recoll needs an aspell version newer than 0.60 for UTF-8 support). The language which is used to build the dictionary out of the index terms (which is done at the end of an indexing pass) is the one defined by your NLS environment. Weird things will probably happen if languages are mixed up.
Note that in cases where Recoll does not know the beginning
          of the string to search for (ie a wildcard expression
          like *coll),
          the expansion can take quite a long time because the full
          index term list will have to be processed. The expansion
          is currently limited at 10000 results for wildcards and
          regular expressions. It is possible to change the limit
          in the configuration file.
Double-clicking on a term in the result list will insert it into the simple search entry field. You can also cut/paste between the result list and any entry field (the end of lines will be taken care of).
See the section describing the use of multiple indexes for generalities. Only the aspects concerning the recoll GUI are described here.
A recoll program instance is always associated with a specific index, which is the one to be updated when requested from the menu, but it can use any number of Recoll indexes for searching. The external indexes can be selected through the external indexes tab in the preferences dialog.
Index selection is performed in two phases. A set of all usable indexes must first be defined, and then the subset of indexes to be used for searching. These parameters are retained across program executions (there are kept separately for each Recoll configuration). The set of all indexes is usually quite stable, while the active ones might typically be adjusted quite frequently.
The main index (defined by RECOLL_CONFDIR) is always active. If this
          is undesirable, you can set up your base configuration to
          index an empty directory.
When adding a new index to the set, you can select either a Recoll configuration directory, or directly a Xapian index directory. In the first case, the Xapian index directory will be obtained from the selected configuration.
As building the set of all indexes can be a little
          tedious when done through the user interface, you can use
          the RECOLL_EXTRA_DBS
          environment variable to provide an initial set. This
          might typically be set up by a system administrator so
          that every user does not have to do it. The variable
          should define a colon-separated list of index
          directories, ie:
export RECOLL_EXTRA_DBS=/some/place/xapiandb:/some/other/db
Another environment variable, RECOLL_ACTIVE_EXTRA_DBS allows adding to
          the active list of indexes. This variable was suggested
          and implemented by a Recoll user. It is mostly useful if
          you use scripts to mount external volumes with
          Recoll indexes. By using
          RECOLL_EXTRA_DBS and
          RECOLL_ACTIVE_EXTRA_DBS, you
          can add and activate the index for the mounted volume
          when starting recoll.
RECOLL_ACTIVE_EXTRA_DBS is
          available for Recoll
          versions 1.17.2 and later. A change was made in the same
          update so that recoll will
          automatically deactivate unreachable indexes when
          starting up.
Documents that you actually view (with the internal preview or an external tool) are entered into the document history, which is remembered.
You can display the history list by using the Tools/Doc History menu entry.
You can erase the document history by using the Erase document history entry in the menu.
The documents in a result list are normally sorted in order of relevance. It is possible to specify a different sort order, either by using the vertical arrows in the GUI toolbox to sort by date, or switching to the result table display and clicking on any header. The sort order chosen inside the result table remains active if you switch back to the result list, until you click one of the vertical arrows, until both are unchecked (you are back to sort by relevance).
Sort parameters are remembered between program invocations, but result sorting is normally always inactive when the program starts. It is possible to keep the sorting activation state between program invocations by checking the Remember sort activation state option in the preferences.
It is also possible to hide duplicate entries inside the result list (documents with the exact same contents as the displayed one). The test of identity is based on an MD5 hash of the document container, not only of the text contents (so that ie, a text document with an image added will not be a duplicate of the text only). Duplicates hiding is controlled by an entry in the GUI configuration dialog, and is off by default.
As of release 1.19, when a result document does have
          undisplayed duplicates, a Dups link will be shown with the result
          list entry. Clicking the link will display the paths
          (URLs + ipaths) for the duplicate entries.
Term completion. Typing Esc Space in the simple search entry field while entering a word will either complete the current word if its beginning matches a unique term in the index, or open a window to propose a list of completions.
Picking up new terms from result or preview text. Double-clicking on a word in the result list or in a preview window will copy it to the simple search entry field.
Wildcards. Wildcards can be used inside search terms in all forms of searches. More about wildcards.
Automatic
            suffixes. Words like odt or ods can be automatically turned into
            query language ext:xxx
            clauses. This can be enabled in the Search preferences panel in the
            GUI.
Disabling stem
            expansion. Entering a capitalized word in any
            search field will prevent stem expansion (no search for
            gardening if you enter
            Garden instead of
            garden). This is the only
            case where character case should make a difference for
            a Recoll search. You
            can also disable stem expansion or change the stemming
            language in the preferences.
Finding related documents. Selecting the Find similar documents entry in the result list paragraph right-click menu will select a set of "interesting" terms from the current result, and insert them into the simple search entry field. You can then possibly edit the list and start a search to find documents which may be apparented to the current result.
File names. File names are added as terms during indexing, and you can specify them as ordinary terms in normal search fields (Recoll used to index all directories in the file path as terms. This has been abandoned as it did not seem really useful). Alternatively, you can use the specific file name search which will only look for file names, and may be faster than the generic search especially when using wildcards.
Phrases
            and Proximity searches. A phrase can be looked
            for by enclosing it in double quotes. Example:
            "user manual" will look
            only for occurrences of user immediately followed by
            manual. You can use the
            This phrase field of the
            advanced search dialog to the same effect. Phrases can
            be entered along simple terms in all simple or advanced
            search entry fields (except This
            exact phrase).
AutoPhrases. This
            option can be set in the preferences dialog. If it is
            set, a phrase will be automatically built and added to
            simple searches when looking for Any terms. This will not change
            radically the results, but will give a relevance boost
            to the results where the search terms appear as a
            phrase. Ie: searching for virtual
            reality will still find all documents where
            either virtual or
            reality or both appear,
            but those which contain virtual
            reality should appear sooner in the list.
Phrase searches can strongly slow down a query if
            most of the terms in the phrase are common. This is why
            the autophrase option is
            off by default for Recoll versions before 1.17. As of
            version 1.17, autophrase
            is on by default, but very common terms will be removed
            from the constructed phrase. The removal threshold can
            be adjusted from the search preferences.
Phrases and
            abbreviations. As of Recoll version 1.17, dotted
            abbreviations like I.B.M.
            are also automatically indexed as a word without the
            dots: IBM. Searching for
            the word inside a phrase (ie: "the IBM company") will only match the
            dotted abrreviation if you increase the phrase slack
            (using the advanced search panel control, or the
            o query language
            modifier). Literal occurences of the word will be
            matched normally.
Using fields. You
            can use the query language
            and field specifications to only search certain parts
            of documents. This can be especially helpful with
            email, for example only searching emails from a
            specific originator: search tips
            from:helpfulgui
Ajusting the result table columns. When displaying results in table mode, you can use a right click on the table headers to activate a pop-up menu which will let you adjust what columns are displayed. You can drag the column headers to adjust their order. You can click them to sort by the field displayed in the column. You can also save the result list in CSV format.
Changing the GUI geometry. It is possible to configure the GUI in wide form factor by dragging the toolbars to one of the sides (their location is remembered between sessions), and moving the category filters to a menu (can be set in the → → panel).
Query explanation. You can get an exact description of what the query looked for, including stem expansion, and Boolean operators used, by clicking on the result list header.
Advanced search history. As of Recoll 1.18, you can display any of the last 100 complex searches performed by using the up and down arrow keys while the advanced search panel is active.
Browsing the result list inside a preview window. Entering Shift-Down or Shift-Up (Shift + an arrow key) in a preview window will display the next or the previous document from the result list. Any secondary search currently active will be executed on the new document.
Scrolling the result list from the keyboard. You can use PageUp and PageDown to scroll the result list, Shift+Home to go back to the first page. These work even while the focus is in the search entry.
Result table: moving the focus to the table. You can use Ctrl-r to move the focus from the search entry to the table, and then use the arrow keys to change the current row. Ctrl-Shift-s returns to the search.
Result table: open / preview. With the focus in the result table, you can use Ctrl-o to open the document from the current row, Ctrl-Shift-o to open the document and close recoll, Ctrl-d to preview the document.
Editing a new search while the focus is not in the search entry. You can use the Ctrl-Shift-S shortcut to return the cursor to the search entry (and select the current search text), while the focus is anywhere in the main window.
Forced
            opening of a preview window. You can use
            Shift+Click on a
            result list Preview link
            to force the creation of a preview window instead of a
            new tab in the existing one.
Closing previews. Entering Ctrl-W in a tab will close it (and, for the last tab, close the preview window). Entering Esc will close the preview window and all its tabs.
Printing previews. Entering Ctrl-P in a preview window will print the currently displayed text.
Quitting. Entering Ctrl-Q almost anywhere will close the application.
Both simple and advanced query dialogs save recent history, but the amount is limited: old queries will eventually be forgotten. Also, important queries may be difficult to find among others. This is why both types of queries can also be explicitely saved to files, from the GUI menus: →
The default location for saved queries is a subdirectory of the current configuration directory, but saved queries are ordinary files and can be written or moved anywhere.
Some of the saved query parameters are part of the
          preferences (e.g. autophrase
          or the active external indexes), and may differ when the
          query is loaded from the time it was saved. In this case,
          Recoll will warn of the
          differences, but will not change the user
          preferences.
You can customize some aspects of the search interface by using the entry in the menu.
There are several tabs in the dialog, dealing with the interface itself, the parameters used for searching and returning results, and what indexes are searched.
Highlight color for query
                terms: Terms from the user query are
                highlighted in the result list samples and the
                preview window. The color can be chosen here. Any
                Qt color string should work (ie red, #ff0000). The default is
                blue.
Style sheet: The
                name of a Qt style
                sheet text file which is applied to the whole
                Recoll application on startup. The default value is
                empty, but there is a skeleton style sheet
                (recoll.qss) inside
                the /usr/share/recoll/examples
                directory. Using a style sheet, you can change most
                recoll graphical
                parameters: colors, fonts, etc. See the sample file
                for a few simple examples.
You should be aware that parameters (e.g.: the background color) set inside the Recoll GUI style sheet will override global system preferences, with possible strange side effects: for example if you set the foreground to a light color and the background to a dark one in the desktop preferences, but only the background is set inside the Recoll style sheet, and it is light too, then text will appear light-on-light inside the Recoll GUI.
Maximum text size highlighted for preview Inserting highlights on search term inside the text before inserting it in the preview window involves quite a lot of processing, and can be disabled over the given text size to speed up loading.
Prefer HTML to plain text for preview if set, Recoll will display HTML as such inside the preview window. If this causes problems with the Qt HTML display, you can uncheck it to display the plain text version instead.
Plain text to HTML line style: when displaying plain text inside the preview window, Recoll tries to preserve some of the original text line breaks and indentation. It can either use PRE HTML tags, which will well preserve the indentation but will force horizontal scrolling for long lines, or use BR tags to break at the original line breaks, which will let the editor introduce other line breaks according to the window width, but will lose some of the original indentation. The third option has been available in recent releases and is probably now the best one: use PRE tags with line wrapping.
Choose editor applicationsr: this opens a dialog which allows you to select the application to be used to open each MIME type. The default is nornally to use the xdg-open utility, but you can override it.
Exceptions: even wen xdg-open is used by default for opening documents, you can set exceptions for MIME types that will still be opened according to Recoll preferences. This is useful for passing parameters like page numbers or search strings to applications that support them (e.g. evince). This cannot be done with xdg-open which only supports passing one parameter.
Document filter choice style: this will let you choose if the document categories are displayed as a list or a set of buttons, or a menu.
Start with simple search
                mode: this lets you choose the value of the
                simple search type on program startup. Either a
                fixed value (e.g. Query
                Language, or the value in use when the
                program last exited.
Auto-start simple search on white space entry: if this is checked, a search will be executed each time you enter a space in the simple search input field. This lets you look at the result list as you enter new terms. This is off by default, you may like it or not...
Start with advanced search dialog open : If you use this dialog frequently, checking the entries will get it to open when recoll starts.
Remember sort activation state if set, Recoll will remember the sort tool stat between invocations. It normally starts with sorting disabled.
Number of results in a result page
Result list font: There is quite a lot of information shown in the result list, and you may want to customize the font and/or font size. The rest of the fonts used by Recoll are determined by your generic Qt config (try the qtconfig command).
Edit result list paragraph format string: allows you to change the presentation of each result list entry. See the result list customisation section.
Edit result page HTML header insert: allows you to define text inserted at the end of the result page HTML header. More detail in the result list customisation section.
Date format: allows specifying the format used for displaying dates inside the result list. This should be specified as an strftime() string (man strftime).
Abstract snippet separator: for synthetic abstracts built from index data, which are usually made of several snippets from different parts of the document, this defines the snippet separator, an ellipsis by default.
Hide duplicate results: decides if result list entries are shown for identical documents found in different places.
Stemming language: stemming obviously depends on the document's language. This listbox will let you chose among the stemming databases which were built during indexing (this is set in the main configuration file), or later added with recollindex -s (See the recollindex manual). Stemming languages which are dynamically added will be deleted at the next indexing pass unless they are also added in the configuration file.
Automatically add phrase
                to simple searches: a phrase will be
                automatically built and added to simple searches
                when looking for Any
                terms. This will give a relevance boost to
                the results where the search terms appear as a
                phrase (consecutive and in order).
Autophrase term frequency threshold percentage: very frequent terms should not be included in automatic phrase searches for performance reasons. The parameter defines the cutoff percentage (percentage of the documents where the term appears).
Replace abstracts from documents: this decides if we should synthesize and display an abstract in place of an explicit abstract found within the document itself.
Dynamically build abstracts: this decides if Recoll tries to build document abstracts (lists of snippets) when displaying the result list. Abstracts are constructed by taking context from the document information, around the search terms.
Synthetic abstract size: adjust to taste...
Synthetic abstract context words: how many words should be displayed around each term occurrence.
Query language magic file
                name suffixes: a list of words which
                automatically get turned into ext:xxx file name suffix clauses
                when starting a query language query (ie:
                doc xls xlsx...). This
                will save some typing for people who use file types
                a lot when querying.
External
          indexes: This panel will let you browse for
          additional indexes that you may want to search. External
          indexes are designated by their database directory (ie:
          /home/someothergui/.recoll/xapiandb,
          /usr/local/recollglobal/xapiandb).
Once entered, the indexes will appear in the External indexes list, and you can chose which ones you want to use at any moment by checking or unchecking their entries.
Your main database (the one the current configuration indexes to), is always implicitly active. If this is not desirable, you can set up your configuration so that it indexes, for example, an empty directory. An alternative indexer may also need to implement a way of purging the index from stale data,
Newer versions of Recoll (from 1.17) normally use WebKit HTML widgets for the result list and the snippets window (this may be disabled at build time). Total customisation is possible with full support for CSS and Javascript. Conversely, there are limits to what you can do with the older Qt QTextBrowser, but still, it is possible to decide what data each result will contain, and how it will be displayed.
The result list presentation can be exhaustively customized by adjusting two elements:
The paragraph format
HTML code inside the header section. For versions 1.21 and later, this is also used for the snippets window
The paragraph format and the header fragment can be edited from the Result list tab of the GUI configuration.
The header fragment is used both for the result list
            and the snippets window. The snippets list is a table
            and has a snippets class
            attribute. Each paragraph in the result list is a
            table, with class respar,
            but this can be changed by editing the paragraph
            format.
There are a few examples on the page about customising the result list on the Recoll web site.
This is an arbitrary HTML string where the
              following printf-like %
              substitutions will be performed:
%A. Abstract
%D. Date
%I. Icon image name.
                    This is normally determined from the MIME type.
                    The associations are defined inside the
                    mimeconf configuration
                    file. If a thumbnail for the file is found
                    at the standard Freedesktop location, this will
                    be displayed instead.
%K. Keywords (if any)
%L. Precooked Preview, Edit, and possibly Snippets links
%M. MIME type
%N. result Number inside the result page
%P. Parent folder Url. In the case of an embedded document, this is the parent folder for the top level container file.
%R. Relevance percentage
%S. Size information
%T. Title or Filename if not set.
%t. Title or Filename if not set.
%U. Url
The format of the Preview, Edit, and Snippets
              links is <a
              href="P%N">, <a
              href="E%N"> and <a
              href="A%N"> where docnum (%N) expands
              to the document number inside the result page).
A link target defined as "F%N" will open the document
              corresponding to the %P
              parent folder expansion, usually creating a file
              manager window on the folder where the container file
              resides. E.g.:
<a href="F%N">%P</a>
A link target defined as R%N|
              will run the corresponding script on the result file
              (if the document is embedded, the script will be
              started on the top-level parent). See the 
              section about defining scripts.scriptname
In addition to the predefined values above, all
              strings like %(fieldname) will be replaced by the
              value of the field named fieldname for this document. Only
              stored fields can be accessed in this way, the value
              of indexed but not stored fields is not known at this
              point in the search process (see field
              configuration). There are currently very few
              fields stored by default, apart from the values above
              (only author and
              filename), so this
              feature will need some custom local configuration to
              be useful. An example candidate would be the
              recipient field which is
              generated by the message input handlers.
The default value for the paragraph format string is:
    "<table class=\"respar\">\n"
    "<tr>\n"
    "<td><a href='%U'><img src='%I' width='64'></a></td>\n"
    "<td>%L  <i>%S</i>   <b>%T</b><br>\n"
    "<span style='white-space:nowrap'><i>%M</i> %D</span>    <i>%U</i> %i<br>\n"
    "%A %K</td>\n"
    "</tr></table>\n"
              You may, for example, try the following for a more web-like experience:
<u><b><a href="P%N">%T</a></b></u><br> %A<font color=#008000>%U - %S</font> - %L
Note that the P%N link in the above paragraph makes the title a preview link. Or the clean looking:
<img src="%I" align="left">%L <font color="#900000">%R</font>   <b>%T&</b><br>%S  <font color="#808080"><i>%U</i></font> <table bgcolor="#e0e0e0"> <tr><td><div>%A</div></td></tr> </table>%K
These samples, and some others are on the web site, with pictures to show how they look.
It is also possible to define the value of the snippet separator inside the abstract section.
The Recoll KIO slave allows performing a Recoll search by entering an appropriate URL in a KDE open dialog, or with an HTML-based interface displayed in Konqueror.
The HTML-based interface is similar to the Qt-based interface, but slightly less powerful for now. Its advantage is that you can perform your search while staying fully within the KDE framework: drag and drop from the result list works normally and you have your normal choice of applications for opening files.
The alternative interface uses a directory view of search results. Due to limitations in the current KIO slave interface, it is currently not obviously useful (to me).
The interface is described in more detail inside a
          help file which you can access by entering recoll:/ inside the konqueror URL line
          (this works only if the recoll KIO slave has been
          previously installed).
The instructions for building this module are located
          in the source tree. See: kde/kio/recoll/00README.txt. Some Linux
          distributions do package the kio-recoll module, so check
          before diving into the build process, maybe it's already
          out there ready for one-click installation.
As a sample application, the Recoll KIO slave could allow preparing a set of HTML documents (for example a manual) so that they become their own search interface inside konqueror.
This can be done by either explicitly inserting
          <a
          href="recoll://..."> links around some document
          areas, or automatically by adding a very small
          javascript program to
          the documents, like the following example, which would
          initiate a search by double-clicking any term:
<script language="JavaScript">
    function recollsearch() {
        var t = document.getSelection();
        window.location.href = 'recoll://search/query?qtp=a&p=0&q=' +
            encodeURIComponent(t);
    }
</script>
 ....
<body ondblclick="recollsearch()">
        There are several ways to obtain search results as a text stream, without a graphical interface:
By passing option -t
              to the recoll program.
By using the recollq program.
By writing a custom Python program, using the Recoll Python API.
The first two methods work in the same way and
        accept/need the same arguments (except for the additional
        -t to recoll). The query to be
        executed is specified as command line arguments.
recollq is
        not built by default. You can use the Makefile in the query directory to build it. This is a
        very simple program, and if you can program a little c++,
        you may find it useful to taylor its output format to your
        needs. Not that recollq is only really useful on systems
        where the Qt libraries (or even the X11 ones) are not
        available. Otherwise, just use recoll
        -t, which takes the exact same parameters and
        options which are described for recollq
recollq
        has a man page (not installed by default, look in the
        doc/man directory). The Usage
        string is as follows:
recollq: usage:
 -P: Show the date span for all the documents present in the index
 [-o|-a|-f] [-q] <query string>
 Runs a recoll query and displays result lines. 
  Default: will interpret the argument(s) as a xesam query string
    query may be like: 
    implicit AND, Exclusion, field spec:    t1 -t2 title:t3
    OR has priority: t1 OR t2 t3 OR t4 means (t1 OR t2) AND (t3 OR t4)
    Phrase: "t1 t2" (needs additional quoting on cmd line)
  -o Emulate the GUI simple search in ANY TERM mode
  -a Emulate the GUI simple search in ALL TERMS mode
  -f Emulate the GUI simple search in filename mode
  -q is just ignored (compatibility with the recoll GUI command line)
Common options:
    -c <configdir> : specify config directory, overriding $RECOLL_CONFDIR
    -d also dump file contents
    -n [first-]<cnt> define the result slice. The default value for [first]
       is 0. Without the option, the default max count is 2000.
       Use n=0 for no limit
    -b : basic. Just output urls, no mime types or titles
    -Q : no result lines, just the processed query and result count
    -m : dump the whole document meta[] array for each result
    -A : output the document abstracts
    -S fld : sort by field <fld>
    -s stemlang : set stemming language to use (must exist in index...)
       Use -s "" to turn off stem expansion
    -D : sort descending
    -i <dbdir> : additional index, several can be given
    -e use url encoding (%xx) for urls
    -F <field name list> : output exactly these fields for each result.
       The field values are encoded in base64, output in one line and 
       separated by one space character. This is the recommended format 
       for use by other programs. Use a normal query with option -m to 
       see the field names.
        Sample execution:
recollq 'ilur -nautique mime:text/html' Recoll query: ((((ilur:(wqf=11) OR ilurs) AND_NOT (nautique:(wqf=11) OR nautiques OR nautiqu OR nautiquement)) FILTER Ttext/html)) 4 results text/html [file:///Users/uncrypted-dockes/projets/bateaux/ilur/comptes.html] [comptes.html] 18593 bytes text/html [file:///Users/uncrypted-dockes/projets/nautique/webnautique/articles/ilur1/index.html] [Constructio... text/html [file:///Users/uncrypted-dockes/projets/pagepers/index.html] [psxtcl/writemime/recoll]... text/html [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/recu-chasse-maree....
In some cases, the document paths stored inside the index do not match the actual ones, so that document previews and accesses will fail. This can occur in a number of circumstances:
When using multiple indexes it is a relatively
              common occurrence that some will actually reside on a
              remote volume, for exemple mounted via NFS. In this
              case, the paths used to access the documents on the
              local machine are not necessarily the same than the
              ones used while indexing on the remote machine. For
              example, /home/me may
              have been used as a topdirs elements while indexing, but
              the directory might be mounted as /net/server/home/me on the local
              machine.
The case may also occur with removable disks. It is perfectly possible to configure an index to live with the documents on the removable disk, but it may happen that the disk is not mounted at the same place so that the documents paths from the index are invalid.
As a last exemple, one could imagine that a big directory has been moved, but that it is currently inconvenient to run the indexer.
More generally, the path translation facility may be useful whenever the documents paths seen by the indexer are not the same as the ones which should be used at query time.
Recoll has a facility for rewriting access paths when extracting the data from the index. The translations can be defined for the main index and for any additional query index.
In the above NFS example, Recoll could be instructed to rewrite
        any file:///home/me URL from
        the index to file:///net/server/home/me, allowing
        accesses from the client.
The translations are defined in the ptrans configuration file, which can
        be edited by hand or from the GUI external indexes
        configuration dialog.
The query language processor is activated in the GUI simple search entry when the search mode selector is set to Query Language. It can also be used with the KIO slave or the command line search. It broadly has the same capabilities as the complex search interface in the GUI.
The language is based on the (seemingly defunct) Xesam user search language specification.
If the results of a query language search puzzle you and
        you doubt what has been actually searched for, you can use
        the GUI Show Query link at the
        top of the result list to check the exact query which was
        finally executed by Xapian.
Here follows a sample request that we are going to explain:
          author:"john doe" Beatles OR Lennon Live OR Unplugged -potatoes
      
        This would search for all documents with John Doe appearing as a
        phrase in the author field (exactly what this is would
        depend on the document type, ie: the From: header, for an email message), and
        containing either beatles or lennon and either
        live or
        unplugged but not
        potatoes (in any
        part of the document).
An element is composed of an optional field
        specification, and a value, separated by a colon (the field
        separator is the last colon in the element). Examples:
        Eugenie,
        author:balzac,
        dc:title:grandet
        dc:title:"eugenie
        grandet"
The colon, if present, means "contains". Xesam defines other relations, which are mostly unsupported for now (except in special cases, described further down).
All elements in the search entry are normally combined
        with an implicit AND. It is possible to specify that
        elements be OR'ed instead, as in Beatles OR Lennon. The OR must be entered literally (capitals),
        and it has priority over the AND associations: word1 word2 OR word3 means word1 AND (word2 OR word3) not (word1 AND word2) OR word3. Explicit parenthesis
        are not
        supported.
As of Recoll 1.21, you can use parentheses to group elements, which will sometimes make things clearer, and may allow expressing combinations which would have been difficult otherwise.
An element preceded by a -
        specifies a term that should not appear.
As usual, words inside quotes define a phrase (the order
        of words is significant), so that title:"prejudice pride" is
        not the same as title:prejudice
        title:pride, and is unlikely to find a
        result.
Words inside phrases and capitalized words are not stem-expanded. Wildcards may be used anywhere inside a term. Specifying a wild-card on the left of a term can produce a very slow search (or even an incorrect one if the expansion is truncated because of excessive size). Also see More about wildcards.
To save you some typing, recent Recoll versions (1.20 and later) interpret a comma-separated list of terms as an AND list inside the field. Use slash characters ('/') for an OR list. No white space is allowed. So
author:john,lennon
will search for documents with john and lennon inside the author field (in any order), and
author:john/ringo
would search for john or
        ringo.
Modifiers can be set on a double-quote value, for
        example to specify a proximity search (unordered). See
        the modifier section. No space
        must separate the final double-quote and the modifiers
        value, e.g. "two
        one"po10
Recoll currently manages the following default fields:
title, subject or caption are synonyms which specify
              data to be searched for in the document title or
              subject.
author or
              from for searching the
              documents originators.
recipient or
              to for searching the
              documents recipients.
keyword for searching
              the document-specified keywords (few documents
              actually have any).
filename for the
              document's file name. This is not necessarily set for
              all documents: internal documents contained inside a
              compound one (for example an EPUB section) do not
              inherit the container file name any more, this was
              replaced by an explicit field (see next).
              Sub-documents can still have a specific filename, if it is implied by the
              document format, for example the attachment file name
              for an email attachment.
containerfilename.
              This is set for all documents, both top-level and
              contained sub-documents, and is always the name of
              the filesystem directory entry which contains the
              data. The terms from this field can only be matched
              by an explicit field specification (as opposed to
              terms from filename
              which are also indexed as general document content).
              This avoids getting matches for all the sub-documents
              when searching for the container file name.
ext specifies the
              file name extension (Ex: ext:html)
Recoll 1.20 and later
        have a way to specify aliases for the field names, which
        will save typing, for example by aliasing filename to fn or containerfilename to cfn. See the section about the
        fields file
The field syntax also supports a few field-like, but special, criteria:
dir for filtering the
              results on file location (Ex: dir:/home/me/somedir). -dir also works to find results not
              in the specified directory (release >= 1.15.8).
              Tilde expansion will be performed as usual (except
              for a bug in versions 1.19 to 1.19.11p1). Wildcards
              will be expanded, but please have a
              look at an important limitation of wildcards in
              path filters.
Relative paths also make sense, for example,
              dir:share/doc would
              match either /usr/share/doc or /usr/local/share/doc
Several dir clauses
              can be specified, both positive and negative. For
              example the following makes sense:
dir:recoll dir:src -dir:utils -dir:common
            
              This would select results which have both
              recoll and src in the path (in any order), and
              which have not either utils or common.
You can also use OR
              conjunctions with dir:
              clauses.
A special aspect of dir clauses is that the values in
              the index are not transcoded to UTF-8, and never
              lower-cased or unaccented, but stored as binary. This
              means that you need to enter the values in the exact
              lower or upper case, and that searches for names with
              diacritics may sometimes be impossible because of
              character set conversion issues. Non-ASCII UNIX file
              paths are an unending source of trouble and are best
              avoided.
You need to use double-quotes around the path value if it contains space characters.
size for filtering
              the results on file size. Example: size<10000. You can use
              <, > or = as operators. You can specify a
              range like the following: size>100 size<1000. The usual
              k/K, m/M, g/G, t/T can
              be used as (decimal) multipliers. Ex: size>1k to search for files
              bigger than 1000 bytes.
date for searching or
              filtering on dates. The syntax for the argument is
              based on the ISO8601 standard for dates and time
              intervals. Only dates are supported, no times. The
              general syntax is 2 elements separated by a
              / character. Each
              element can be a date or a period of time. Periods
              are specified as PnYnMnD. The n numbers are the
              respective numbers of years, months or days, any of
              which may be missing. Dates are specified as
              YYYY-MM-DD. The days and
              months parts may be missing. If the / is present but an element is
              missing, the missing element is interpreted as the
              lowest or highest date in the index. Examples:
2001-03-01/2002-05-01 the
                    basic syntax for an interval of dates.
2001-03-01/P1Y2M the same
                    specified with a period.
2001/ from the
                    beginning of 2001 to the latest date in the
                    index.
2001 the whole
                    year of 2001
P2D/ means 2
                    days ago up to now if there are no documents
                    with dates in the future.
/2003 all
                    documents from 2003 or older.
Periods can also be specified with small letters (ie: p2y).
mime or format for specifying the MIME type.
              This one is quite special because you can specify
              several values which will be OR'ed (the normal
              default for the language is AND). Ex: mime:text/plain mime:text/html.
              Specifying an explicit boolean operator before a
              mime specification is
              not supported and will produce strange results. You
              can filter out certain types by using negation
              (-mime:some/type), and
              you can use wildcards in the value (mime:text/*). Note that mime is the ONLY field with an OR
              default. You do need to use OR with ext terms for example.
type or rclcat for specifying the category
              (as in text/media/presentation/etc.). The
              classification of MIME types in categories is defined
              in the Recoll
              configuration (mimeconf), and can be modified or
              extended. The default category names are those which
              permit filtering results in the main GUI screen.
              Categories are OR'ed like MIME types above. This
              can't be negated with -
              either.
The document input handlers used while indexing have the possibility to create other fields with arbitrary names, and aliases may be defined in the configuration, so that the exact field search possibilities may be different for you if someone took care of the customisation.
Some characters are recognized as search modifiers
          when found immediately after the closing double quote of
          a phrase, as in "some
          term"modifierchars. The actual "phrase" can be a
          single term of course. Supported modifiers:
l can be used to
                turn off stemming (mostly makes sense with
                p because stemming is
                off by default for phrases).
o can be used to
                specify a "slack" for phrase and proximity
                searches: the number of additional terms that may
                be found between the specified ones. If
                o is followed by an
                integer number, this is the slack, else the default
                is 10.
p can be used to
                turn the default phrase search into a proximity one
                (unordered). Example:"order
                any in"p
C will turn on case
                sensitivity (if the index supports it).
D will turn on
                diacritics sensitivity (if the index supports
                it).
A weight can be specified for a query element by
                specifying a decimal value at the start of the
                modifiers. Example: "Important"2.5.
For Recoll versions 1.18 and later, and when working with a raw index (not the default), searches can be made sensitive to character case and diacritics. How this happens is controlled by configuration variables and what search data is entered.
The general default is that searches are insensitive to
        case and diacritics. An entry of resume will match any of Resume, RESUME, résumé, Résumé etc.
Two configuration variables can automate switching on sensitivity:
If this is set, search sensitivity to diacritics
              will be turned on as soon as an accented character
              exists in a search term. When the variable is set to
              true, resume will start
              a diacritics-unsensitive search, but résumé will be matched
              exactly. The default value is false.
If this is set, search sensitivity to character
              case will be turned on as soon as an upper-case
              character exists in a search term except for the first one.
              When the variable is set to true, us or Us will start a
              diacritics-unsensitive search, but US will be matched exactly. The
              default value is true (contrary to
              autodiacsens).
As in the past, capitalizing the first letter of a word will turn off its stem expansion and have no effect on case-sensitivity.
You can also explicitely activate case and diacritics
        sensitivity by using modifiers with the query language.
        C will make the term
        case-sensitive, and D will
        make it diacritics-sensitive. Examples:
        "us"C
   
        will search for the term us
        exactly (Us will not be a
        match).
        "resume"D
      
        will search for the term resume exactly (résumé will not be a
        match).
When either case or diacritics sensitivity is activated, stem expansion is turned off. Having both does not make much sense.
Some special characters are interpreted by Recoll in search strings to expand or specialize the search. Wildcards expand a root term in controlled ways. Anchor characters can restrict a search to succeed only if the match is found at or near the beginning of the document or one of its fields.
All words entered in Recoll search fields will be processed for wildcard expansion before the request is finally executed.
The wildcard characters are:
* which matches 0
                or more characters.
? which matches a
                single character.
[] which allow
                defining sets of characters to be matched (ex:
                [abc] matches a single character which
                may be 'a' or 'b' or 'c', [0-9] matches any number.
You should be aware of a few things when using wildcards.
Using a wildcard character at the beginning of a
                word can make for a slow search because
                Recoll will have
                to scan the whole index term list to find the
                matches. However, this is much less a problem for
                field searches, and queries like author:*@domain.com
                can sometimes be very useful.
For Recoll version 18 only, when working with a raw index (preserving character case and diacritics), the literal part of a wildcard expression will be matched exactly for case and diacritics. This is not true any more for versions 19 and later.
Using a * at the
                end of a word can produce more matches than you
                would think, and strange search results. You can
                use the term
                explorer tool to check what completions exist
                for a given term. You can also see exactly what
                search was performed by clicking on the link at the
                top of the result list. In general, for natural
                language terms, stem expansion will produce better
                results than an ending * (stem expansion is turned off
                when any wildcard character appears in the
                term).
Due to the way that Recoll processes wildcards inside
            dir path filtering
            clauses, they will have a multiplicative effect on the
            query size. A clause containg wildcards in several
            paths elements, like, for example, dir:/home/me/*/*/docdir,
            will almost certainly fail if your indexed tree is of
            any realistic size.
Depending on the case, you may be able to work
            around the issue by specifying the paths elements more
            narrowly, with a constant prefix, or by using 2
            separate dir: clauses
            instead of multiple wildcards, as in dir:/home/me dir:docdir. The latter
            query is not equivalent to the initial one because it
            does not specify a number of directory levels, but
            that's the best we can do (and it may be actually more
            useful in some cases).
Two characters are used to specify that a search hit
          should occur at the beginning or at the end of the text.
          ^ at the beginning of a term
          or phrase constrains the search to happen at the start,
          $ at the end force it to
          happen at the end.
As this function is implemented as a phrase search it is possible to specify a maximum distance at which the hit should occur, either through the controls of the advanced search panel, or using the query language, for example, as in:
"^someterm"o10
which would force someterm to be found within 10 terms of
          the start of the text. This can be combined with a field
          search as in somefield:"^someterm"o10 or somefield:someterm$.
This feature can also be used with an actual phrase
          search, but in this case, the distance applies to the
          whole phrase and anchor, so that, for example,
          bla bla my unexpected term
          at the beginning of the text would be a match for
          "^my term"o5.
Anchored searches can be very useful for searches inside somewhat structured documents like scientific articles, in case explicit metadata has not been supplied (a most frequent case), for example for looking for matches inside the abstract or the list of authors (which occur at the top of the document).
Being independant of the desktop type has its drawbacks: Recoll desktop integration is minimal. However there are a few tools available:
The KDE KIO Slave was described in a previous section.
If you use a recent version of Ubuntu Linux, you may find the Ubuntu Unity Lens module useful.
There is also an independantly developed Krunner plugin.
Here follow a few other things that may help.
It is surprisingly convenient to be able to show or hide the Recoll GUI with a single keystroke. Recoll comes with a small Python script, based on the libwnck window manager interface library, which will allow you to do just this. The detailed instructions are on this wiki page.
This is probably obsolete now. Anyway:
The Recoll source tree contains the source code to the recoll_applet, a small application derived from the find_applet. This can be used to add a small Recoll launcher to the KDE panel.
The applet is not automatically built with the main
          Recoll programs, nor is
          it included with the main source distribution (because
          the KDE build boilerplate makes it relatively big). You
          can download its source from the recoll.org download
          page. Use the omnipotent configure;make;make
          install incantation to build and
          install.
You can then add the applet to the panel by right-clicking the panel and choosing the Add applet entry.
The recoll_applet has a small text window where you can type a Recoll query (in query language form), and an icon which can be used to restrict the search to certain types of files. It is quite primitive, and launches a new recoll GUI instance every time (even if it is already running). You may find it useful anyway.
Recoll has an Application Programming Interface, usable both for indexing and searching, currently accessible from the Python language.
Another less radical way to extend the application is to write input handlers for new types of documents.
The processing of metadata attributes for documents
      (fields) is highly
      configurable.
filters, which is still
          reflected in the name of the directory which holds them
          and many configuration variables. They were named this
          way because one of their primary functions is to filter
          out the formatting directives and keep the text content.
          However these modules may have other behaviours, and the
          term input handler is now
          progressively substituted in the documentation.
          filter is still used in many
          places though.
        Recoll input handlers cooperate to translate from the multitude of input document formats, simple ones as opendocument, acrobat), or compound ones such as Zip or Email, into the final Recoll indexing input format, which is plain text. Most input handlers are executable programs or scripts. A few handlers are coded in C++ and live inside recollindex. This latter kind will not be described here.
There are currently (1.18 and since 1.13) two kinds of external executable input handlers:
Simple exec handlers
              run once and exit. They can be bare programs like
              antiword, or
              scripts using other programs. They are very simple to
              write, because they just need to print the converted
              document to the standard output. Their output can be
              plain text or HTML. HTML is usually preferred because
              it can store metadata fields and it allows preserving
              some of the formatting for the GUI preview.
Multiple execm
              handlers can process multiple files (sparing the
              process startup time which can be very significant),
              or multiple documents per file (e.g.: for
              zip or chm files). They communicate
              with the indexer through a simple protocol, but are
              nevertheless a bit more complicated than the older
              kind. Most of new handlers are written in
              Python, using a
              common module to handle the protocol. There is an
              exception, rclimg which is
              written in Perl. The subdocuments output by these
              handlers can be directly indexable (text or HTML), or
              they can be other simple or compound documents that
              will need to be processed by another handler.
In both cases, handlers deal with regular file system files, and can process either a single document, or a linear list of documents in each file. Recoll is responsible for performing up to date checks, deal with more complex embedding and other upper level issues.
A simple handler returning a document in text/plain format, can transfer no
        metadata to the indexer. Generic metadata, like document
        size or modification date, will be gathered and stored by
        the indexer.
Handlers that produce text/html format can return an arbitrary
        amount of metadata inside HTML meta tags. These will be processed
        according to the directives found in the fields configuration file.
The handlers that can handle multiple documents per file
        return a single piece of data to identify each document
        inside the file. This piece of data, called an ipath element will be sent back by
        Recoll to extract the
        document at query time, for previewing, or for creating a
        temporary file to be opened by a viewer.
The following section describes the simple handlers, and
        the next one gives a few explanations about the
        execm ones. You could
        conceivably write a simple handler with only the elements
        in the manual. This will not be the case for the other
        ones, for which you will have to look at the code.
Recoll simple handlers are usually shell-scripts, but this is in no way necessary. Extracting the text from the native format is the difficult part. Outputting the format expected by Recoll is trivial. Happily enough, most document formats have translators or text extractors which can be called from the handler. In some cases the output of the translating program is completely appropriate, and no intermediate shell-script is needed.
Input handlers are called with a single argument which is the source file name. They should output the result to stdout.
When writing a handler, you should decide if it will output plain text or HTML. Plain text is simpler, but you will not be able to add metadata or vary the output character encoding (this will be defined in a configuration file). Additionally, some formatting may be easier to preserve when previewing HTML. Actually the deciding factor is metadata: Recoll has a way to extract metadata from the HTML header and use it for field searches..
The RECOLL_FILTER_FORPREVIEW environment
          variable (values yes,
          no) tells the handler if the
          operation is for indexing or previewing. Some handlers
          use this to output a slightly different format, for
          example stripping uninteresting repeated keywords (ie:
          Subject: for email) when
          indexing. This is not essential.
You should look at one of the simple handlers, for example rclps for a starting point.
Don't forget to make your handler executable before testing !
If you can program and want to write an execm handler, it should not be too
          difficult to make sense of one of the existing modules.
          For example, look at rclzip which uses Zip
          file paths as identifiers (ipath), and rclics, which uses an
          integer index. Also have a look at the comments inside
          the internfile/mh_execm.h
          file and possibly at the corresponding module.
execm handlers sometimes
          need to make a choice for the nature of the ipath elements that they use in
          communication with the indexer. Here are a few
          guidelines:
Use ASCII or UTF-8 (if the identifier is an integer print it, for example, like printf %d would do).
If at all possible, the data should make some kind of sense when printed to a log file to help with debugging.
Recoll uses a
                colon (:) as a
                separator to store a complex path internally (for
                deeper embedding). Colons inside the ipath elements output by a handler
                will be escaped, but would be a bad choice as a
                handler-specific separator (mostly, again, for
                debugging issues).
In any case, the main goal is that it should be easy
          for the handler to extract the target document, given the
          file name and the ipath
          element.
execm handlers will also
          produce a document with a null ipath element. Depending on the type of
          document, this may have some associated data (e.g. the
          body of an email message), or none (typical for an
          archive file). If it is empty, this document will be
          useful anyway for some operations, as the parent of the
          actual data documents.
There are two elements that link a file to the handler which should process it: the association of file to MIME type and the association of a MIME type with a handler.
The association of files to MIME types is mostly based
          on name suffixes. The types are defined inside the
          mimemap file. Example:
.doc = application/msword
If no suffix association is found for the file name, Recoll will try to execute the file -i command to determine a MIME type.
The association of file types to handlers is performed
          in the mimeconf file. A sample will
          probably be of better help than a long explanation:
[index]
application/msword = exec antiword -t -i 1 -m UTF-8;\
     mimetype = text/plain ; charset=utf-8
application/ogg = exec rclogg
text/rtf = exec unrtf --nopict --html; charset=iso-8859-1; mimetype=text/html
application/x-chm = execm rclchm
          The fragment specifies that:
application/msword
                files are processed by executing the antiword program,
                which outputs text/plain encoded in utf-8.
application/ogg
                files are processed by the rclogg script,
                with default output type (text/html, with encoding specified
                in the header, or utf-8 by default).
text/rtf is
                processed by unrtf, which
                outputs text/html. The
                iso-8859-1 encoding is
                specified because it is not the utf-8 default, and not output by
                unrtf
                in the HTML header section.
application/x-chm
                is processed by a persistant handler. This is
                determined by the execm keyword.
The output HTML could be very minimal like the following example:
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
  </head>
  <body>
   Some text content
  </body>
</html>
          
          You should take care to escape some characters inside
          the text by transforming them into appropriate entities.
          At the very minimum, "&"
          should be transformed into "&", "<" should be transformed into
          "<". This is not
          always properly done by translating programs which output
          HTML, and of course never by those which output plain
          text.
When encapsulating plain text in an HTML body, the
          display of a preview may be improved by enclosing the
          text inside <pre>
          tags.
The character set needs to be specified in the header. It does not need to be UTF-8 (Recoll will take care of translating it), but it must be accurate for good results.
Recoll will process
          meta tags inside the header
          as possible document fields candidates. Documents fields
          can be processed by the indexer in different ways, for
          searching or displaying inside query results. This is
          described in a following
          section.
By default, the indexer will process the standard
          header fields if they are present: title, meta/description, and meta/keywords are both indexed and
          stored for query-time display.
A predefined non-standard meta tag will also be processed by
          Recoll without further
          configuration: if a date tag
          is present and has the right format, it will be used as
          the document date (for display and sorting), in
          preference to the file modification date. The date format
          should be as follows:
<meta name="date" content="YYYY-mm-dd HH:MM:SS">
or
<meta name="date" content="YYYY-mm-ddTHH:MM:SS">
          
          Example:
<meta name="date" content="2013-02-24 17:50:00">
          
          Input handlers also have the possibility to "invent" field names. This should also be output as meta tags:
<meta name="somefield" content="Some textual data" />
You can embed HTML markup inside the content of custom
          fields, for improving the display inside result lists. In
          this case, add a (wildly non-standard) markup attribute to tell Recoll that the value is HTML and
          should not be escaped for display.
<meta name="somefield" markup="html" content="Some <i>textual</i> data" />
As written above, the processing of fields is described in a further section.
Fields are named pieces of
        information in or about documents, like title, author, abstract.
The field values for documents can appear in several
        ways during indexing: either output by input handlers as
        meta fields in the HTML header
        section, or extracted from file extended attributes, or
        added as attributes of the Doc
        object when using the API, or again synthetized internally
        by Recoll.
The Recoll query language allows searching for text in a specific field.
Recoll defines a number
        of default fields. Additional ones can be output by
        handlers, and described in the fields configuration file.
Fields can be:
indexed, meaning that
              their terms are separately stored in inverted lists
              (with a specific prefix), and that a field-specific
              search is possible.
stored, meaning that
              their value is recorded in the index data record for
              the document, and can be returned and displayed with
              search results.
A field can be either or both indexed and stored. This
        and other aspects of fields handling is defined inside the
        fields configuration
        file.
The sequence of events for field processing is as follows:
During indexing, recollindex scans
              all meta fields in HTML
              documents (most document types are transformed into
              HTML at some point). It compares the name for each
              element to the configuration defining what should be
              done with fields (the fields file)
If the name for the meta element matches one for a field
              that should be indexed, the contents are processed
              and the terms are entered into the index with the
              prefix defined in the fields file.
If the name for the meta element matches one for a field
              that should be stored, the content of the element is
              stored with the document data record, from which it
              can be extracted and displayed at query time.
At query time, if a field search is performed, the index prefix is computed and the match is only performed against appropriately prefixed terms in the index.
At query time, the field can be displayed inside the result list by using the appropriate directive in the definition of the result list paragraph format. All fields are displayed on the fields screen of the preview window (which you can reach through the right-click menu). This is independant of the fact that the search which produced the results used the field or not.
You can find more information in the section about the
        fields file, or in
        comments inside the file.
You can also have a look at the example on the Wiki, detailing how one could add a page count field to pdf documents for displaying inside result lists.
A few elements in the interface are specific and and need an explanation.
An udi (unique document identifier) identifies a document. Because of limitations inside the index engine, it is restricted in length (to 200 bytes), which is why a regular URI cannot be used. The structure and contents of the udi is defined by the application and opaque to the index engine. For example, the internal file system indexer uses the complete document path (file path + internal path), truncated to length, the suppressed part being replaced by a hash value.
This data value (set as a field in the Doc
                object) is stored, along with the URL, but not
                indexed by Recoll.
                Its contents are not interpreted, and its use is up
                to the application. For example, the Recoll internal file system
                indexer stores the part of the document access path
                internal to the container file (ipath in this case is a list of
                subdocument sequential numbers). url and ipath are
                returned in every search result and permit access
                to the original document.
The fields file
                inside the Recoll
                configuration defines which document fields are
                either "indexed" (searchable), "stored"
                (retrievable with search results), or both.
Data for an external indexer, should be stored in a separate index, not the one for the Recoll internal file system indexer, except if the latter is not used at all). The reason is that the main document indexer purge pass would remove all the other indexer's documents, as they were not seen during indexing. The main indexer documents would also probably be a problem for the external indexer purge operation.
Recoll versions after 1.11 define a Python programming interface, both for searching and indexing. The indexing portion has seen little use, but the searching one is used in the Recoll Ubuntu Unity Lens and Recoll Web UI.
The API is inspired by the Python database API specification. There were two major changes in recent Recoll versions:
recoll module became a package
                (with an internal recoll module) as of Recoll version 1.19, in order
                to add more functions. For existing code, this only
                changes the way the interface must be
                imported.We will mostly describe the new API and package structure here. A paragraph at the end of this section will explain a few differences and ways to write code compatible with both versions.
The Python interface can be found in the source
            package, under python/recoll.
The python/recoll/
            directory contains the usual setup.py. After configuring the main
            Recoll code, you can
            use the script to build and install the Python
            module:
            cd recoll-xxx/python/recoll
            python setup.py build
            python setup.py install
          
            The normal Recoll installer installs the Python API along with the main code.
When installing from a repository, and depending on the distribution, the Python API can sometimes be found in a separate package.
The recoll package
            contains two modules:
The recoll module
                  contains functions and classes used to query (or
                  update) the index.
The rclextract
                  module contains functions and classes used to
                  access document data.
connect()
                    function connects to one or several
                    Recoll
                    index(es) and returns a Db object.
                    confdir may specify a
                        configuration directory. The usual defaults
                        apply.extra_dbs is a list of
                        additional indexes (Xapian
                        directories).writable decides if we can
                        index new data through this
                        connection.A Db object is created by a connect() call and holds a
                connection to a Recoll index.
Methods
Db object after this.Query object for this
                    index.maxchars defines
                    the maximum total size of the abstract.
                    contextwords
                    defines how many terms are shown around the
                    keyword.match_type can be either of
                    wildcard,
                    regexp or
                    stem. Returns a
                    list of terms expanded from the input
                    expression.A Query object
                (equivalent to a cursor in the Python DB API) is
                created by a Db.query() call. It is used to
                execute index searches.
Methods
fieldname, in
                    ascending or descending order. Must be called
                    before executing the search.query_string, a
                    Recoll search
                    language string.Doc objects in the current
                    search results, and returns them as an array of
                    the required size, which is by default the
                    value of the arraysize data member.Doc object from the current
                    search results.mode can be
                    relative or
                    absolute.ishtml can be set
                    to indicate that the input text is HTML and
                    that HTML special characters should not be
                    escaped. methods
                    if set should be an object with methods
                    startMatch(i) and endMatch() which will be
                    called for each match and should return a begin
                    and end tagdoc (a Doc object) by selecting text
                    around the match terms. If methods is set, will
                    also perform highlighting. See the highlight
                    method.for doc in query: will
                    work.Data descriptors
scroll()). Starts at 0.A Doc object
                contains index data for a given document. The data
                is extracted from the index when searching, or set
                by the indexer program when updating. The Doc
                object has many attributes to be read or set by its
                user. It matches exactly the Rcl::Doc C++ object.
                Some of the attributes are predefined, but,
                especially when indexing, others can be set, the
                name of which will be processed as field names by
                the indexing configuration. Inputs can be specified
                as Unicode or strings. Outputs are Unicode objects.
                All dates are specified as Unix timestamps, printed
                as strings. Please refer to the rcldb/rcldoc.h C++ file for a
                description of the predefined attributes.
At query time, only the fields that are defined
                as stored either by
                default or in the fields configuration file will be
                meaningful in the Doc
                object. Especially this will not be the case for
                the document text. See the rclextract module for accessing
                document contents.
Methods
A SearchData object
                allows building a query by combining clauses, for
                execution by Query.executesd(). It can be used
                in replacement of the query language approach. The
                interface is going to change a little, so no
                detailed doc for now...
Methods
Index queries do not provide document content (only
            a partial and unprecise reconstruction is performed to
            show the snippets text). In order to access the actual
            document data, the data extraction part of the indexing
            process must be performed (subdocument access and
            format translation). This is not trivial in general.
            The rclextract module
            currently provides a single class which can be used to
            access the data content for result documents.
Methods
Extractor
                    object is built from a Doc object, output from a
                    query.ipath and
                      return a Doc
                      object. The doc.text field has the document
                      text converted to either text/plain or
                      text/html according to doc.mimetype. The
                      typical use would be as follows:
                      qdoc = query.fetchone() extractor = recoll.Extractor(qdoc) doc = extractor.textextract(qdoc.ipath) # use doc.text, e.g. for previewing
qdoc = query.fetchone() extractor = recoll.Extractor(qdoc) filename = extractor.idoctofile(qdoc.ipath, qdoc.mimetype)
The following sample would query the index with a
            user language string. See the python/samples directory inside the
            Recoll source for
            other examples. The recollgui subdirectory has a very
            embryonic GUI which demonstrates the highlighting and
            data extraction functions.
#!/usr/bin/env python
from recoll import recoll
db = recoll.connect()
db.setAbstractParams(maxchars=80, contextwords=4)
query = db.query()
nres = query.execute("some user question")
print "Result count: ", nres
if nres > 5:
    nres = 5
for i in range(nres):
    doc = query.fetchone()
    print "Result #%d" % (query.rownumber,)
    for k in ("title", "size"):
        print k, ":", getattr(doc, k).encode('utf-8')
    abs = db.makeDocAbstract(doc, query).encode('utf-8')
    print abs
    print
          The following code fragments can be used to ensure that code can run with both the old and the new API (as long as it does not use the new abilities of the new API of course).
Adapting to the new package structure:
try:
    from recoll import recoll
    from recoll import rclextract
    hasextract = True
except:
    import recoll
    hasextract = False
            Adapting to the change of nature of the next Query member. The same test can be
            used to choose to use the scroll() method (new) or set the
            next value (old).
       rownum = query.next if type(query.next) == int else \
                 query.rownumber
          Recoll binary copies are always distributed as regular packages for your system. They can be obtained either through the system's normal software distribution framework (e.g. Debian/Ubuntu apt, FreeBSD ports, etc.), or from some type of "backports" repository providing versions newer than the standard ones, or found on the Recoll WEB site in some cases.
There used to exist another form of binary install, as pre-compiled source trees, but these are just less convenient than the packages and don't exist any more.
The package management tools will usually automatically deal with hard dependancies for packages obtained from a proper package repository. You will have to deal with them by hand for downloaded packages (for example, when dpkg complains about missing dependancies).
In all cases, you will have to check or install supporting applications for the file types that you want to index beyond those that are natively processed by Recoll (text, HTML, email files, and a few others).
You should also maybe have a look at the configuration section (but this may not be necessary for a quick test with default parameters). Most parameters can be more conveniently set from the GUI interface.
Recoll uses external applications to index some file types. You need to install them for the file types that you wish to have indexed (these are run-time optional dependencies. None is needed for building or running Recoll except for indexing their specific file type).
After an indexing pass, the commands that were found
        missing can be displayed from the recoll File menu. The list is stored in the
        missing text file inside the
        configuration directory.
A list of common file types which need external commands follows. Many of the handlers need the iconv command, which is not always listed as a dependancy.
Please note that, due to the relatively dynamic nature of this information, the most up to date version is now kept on http://www.recoll.org/features.html along with links to the home pages or best source/patches pages, and misc tips. The list below is not updated often and may be quite stale.
For many Linux distributions, most of the commands listed can be installed from the package repositories. However, the packages are sometimes outdated, or not the best version for Recoll, so you should take a look at http://www.recoll.org/features.html if a file type is important to you.
As of Recoll release 1.14, a number of XML-based formats that were handled by ad hoc handler code now use the xsltproc command, which usually comes with libxslt. These are: abiword, fb2 (ebooks), kword, openoffice, svg.
Now for the list:
Openoffice files need unzip and xsltproc.
PDF files need pdftotext which is
              part of Poppler
              (usually comes with the poppler-utils package). Avoid the
              original one from Xpdf.
Postscript files need pstotext. The original version has an issue with shell character in file names, which is corrected in recent packages. See http://www.recoll.org/features.html for more detail.
MS Word needs antiword. It is also useful to have wvWare installed as it may be be used as a fallback for some files which antiword does not handle.
MS Excel and PowerPoint are processed by internal Python handlers.
MS Open XML (docx) needs xsltproc.
Wordperfect files need wpd2html from the libwpd (or libwpd-tools on Ubuntu) package.
RTF files need unrtf, which, in its older versions, has much trouble with non-western character sets. Many Linux distributions carry outdated unrtf versions. Check http://www.recoll.org/features.html for details.
TeX files need untex or detex. Check http://www.recoll.org/features.html for sources if it's not packaged for your distribution.
dvi files need dvips.
djvu files need djvutxt and djvused from the DjVuLibre package.
Audio files: Recoll releases 1.14 and later use a single Python handler based on mutagen for all audio file types.
Pictures: Recoll uses the Exiftool Perl package to extract tag information. Most image file formats are supported. Note that there may not be much interest in indexing the technical tags (image size, aperture, etc.). This is only of interest if you store personal tags or textual descriptions inside the image files.
chm: files in Microsoft help format need Python and the pychm module (which needs chmlib).
ICS: up to Recoll 1.13, iCalendar files need Python and the icalendar module. icalendar is not needed for newer versions, which use internal code.
Zip archives need Python (and the standard zipfile module).
Rar archives need Python, the rarfile Python module and the unrar utility.
Midi karaoke files need Python and the Midi module
Konqueror webarchive format with Python (uses the Tarfile module).
Mimehtml web archive format (support based on the email handler, which introduces some mild weirdness, but still usable).
Text, HTML, email folders, and Scribus files are processed internally. Lyx is used to index Lyx files. Many handlers need iconv and the standard sed and awk.
If you can install any or all of the following through the package manager for your system, all the better. Especially Qt is a very big piece of software, but you will most probably be able to find a binary package.
You may have to compile Xapian but this is easy.
The shopping list:
C++ compiler. Up to Recoll version 1.13.04, its absence can manifest itself by strange messages about a missing iconv_open.
Development files for Xapian core.
If you are building Xapian for an older CPU
                  (before Pentium 4 or Athlon 64), you need to add
                  the --disable-sse
                  flag to the configure command. Else all Xapian
                  application will crash with an illegal instruction error.
Development files for Qt 4 . Recoll has not been tested with Qt 5 yet. Recoll 1.15.9 was the last version to support Qt 3. If you do not want to install or build the Qt Webkit module, Recoll has a configuration option to disable its use (see further).
Development files for X11 and zlib.
You may also need libiconv. On Linux systems, the iconv interface is part of libc and you should not need to do anything special.
Check the Recoll download page for up to date version information.
Recoll has been built on Linux, FreeBSD, Mac OS X, and Solaris, most versions after 2005 should be ok, maybe some older ones too (Solaris 8 is ok). If you build on another system, and need to modify things, I would very much welcome patches.
Configure options:
--without-aspell
                will disable the code for phonetic matching of
                search terms.
--with-fam or
                --with-inotify will
                enable the code for real time indexing. Inotify
                support is enabled by default on recent Linux
                systems.
--with-qzeitgeist
                will enable sending Zeitgeist events about the
                visited search results, and needs the qzeitgeist package.
--disable-webkit is
                available from version 1.17 to implement the result
                list with a Qt
                QTextBrowser instead of a WebKit widget if you do
                not or can't depend on the latter.
--disable-idxthreads
                is available from version 1.19 to suppress
                multithreading inside the indexing process. You can
                also use the run-time configuration to restrict
                recollindex to
                using a single thread, but the compile-time option
                may disable a few more unused locks. This only
                applies to the use of multithreading for the core
                index processing (data input). The Recoll monitor mode always
                uses at least two threads of execution.
--disable-python-module will avoid
                building the Python module.
--disable-xattr will
                prevent fetching data from file extended
                attributes. Beyond a few standard attributes,
                fetching extended attributes data can only be
                useful is some application stores data in there,
                and also needs some simple configuration (see
                comments in the fields configuration file).
--enable-camelcase
                will enable splitting camelCase words.
                This is not enabled by default as it has the
                unfortunate side-effect of making some phrase
                searches quite confusing: ie, "MySQL manual" would be matched by
                "MySQL manual" and
                "my sql manual" but
                not "mysql manual"
                (only inside phrase searches).
--with-file-command
                Specify the version of the 'file' command to use
                (ie: --with-file-command=/usr/local/bin/file). Can
                be useful to enable the gnu version on systems
                where the native one is bad.
--disable-qtgui
                Disable the Qt interface. Will allow building the
                indexer and the command line search program in
                absence of a Qt environment.
--disable-x11mon
                Disable X11
                connection monitoring inside recollindex. Together
                with --disable-qtgui, this allows building recoll
                without Qt and
                X11.
--disable-pic will
                compile Recoll
                with position-dependant code. This is incompatible
                with building the KIO or the Python or PHP extensions, but might
                yield very marginally faster code.
Of course the usual autoconf configure
                options, like --prefix
                apply.
Normal procedure:
        cd recoll-xxx
        ./configure
        make
        (practices usual hardship-repelling invocations)
      
          There is little auto-configuration. The configure script will
          mainly link one of the system-specific files in the
          mk directory to
          mk/sysconf. If your system
          is not known yet, it will tell you as much, and you may
          want to manually copy and modify one of the existing
          files (the new file name should be the output of
          uname
          -s).
We did not test building the GUI on Solaris for recent versions. You will need at least Qt 4.4. There are some hints on an old web site page, they may still be valid.
Someone did test the 1.19 indexer and Python module build, they do work, with a few minor glitches. Be sure to use GNU make and install.
Either type make
          install or execute recollinstall ,
          in the root of the source tree. This will copy the
          commands to prefixprefix/binprefix/share/recoll
If the installation prefix given to recollinstall is
          different from either the system default or the value
          which was specified when executing configure (as in
          configure --prefix
          /some/path), you will have to set the
          RECOLL_DATADIR environment
          variable to indicate where the shared data is to be found
          (ie for (ba)sh: export
          RECOLL_DATADIR=/some/path/share/recoll).
You can then proceed to configuration.
Most of the parameters specific to the recoll GUI are set
        through the Preferences menu
        and stored in the standard Qt place ($HOME/.config/Recoll.org/recoll.conf).
        You probably do not want to edit this by hand.
Recoll indexing options are set inside text configuration files located in a configuration directory. There can be several such directories, each of which defines the parameters for one index.
The configuration files can be edited by hand or through the Index configuration dialog (Preferences menu). The GUI tool will try to respect your formatting and comments as much as possible, so it is quite possible to use both ways.
The most accurate documentation for the configuration parameters is given by comments inside the default files, and we will just give a general overview here.
By default, for each index, there are two sets of
        configuration files. System-wide configuration files are
        kept in a directory named like /usr/[local/]share/recoll/examples, and
        define default values, shared by all indexes. For each
        index, a parallel set of files defines the customized
        parameters.
In addition (as of Recoll version 1.19.7), it is possible
        to specify two additional configuration directories which
        will be stacked before and after the user configuration
        directory. These are defined by the RECOLL_CONFTOP and RECOLL_CONFMID environment variables. Values
        from configuration files inside the top directory will
        override user ones, values from configuration files inside
        the middle directory will override system ones and be
        overriden by user ones. These two variables may be of use
        to applications which augment Recoll functionality, and need to add
        configuration data without disturbing the user's files.
        Please note that the two, currently single, values will
        probably be interpreted as colon-separated lists in the
        future: do not use colon characters inside the directory
        paths.
The default location of the configuration is the
        .recoll directory in your
        home. Most people will only use this directory.
This location can be changed, or others can be added
        with the RECOLL_CONFDIR
        environment variable or the -c
        option parameter to recoll and recollindex.
If the .recoll directory
        does not exist when recoll or recollindex are started,
        it will be created with a set of empty configuration files.
        recoll will
        give you a chance to edit the configuration file before
        starting indexing. recollindex will proceed
        immediately. To avoid mistakes, the automatic directory
        creation will only occur for the default location, not if
        -c or RECOLL_CONFDIR were used (in the latter
        cases, you will have to create the directory).
All configuration files share the same format. For example, a short extract of the main configuration file might look as follows:
        # Space-separated list of directories to index.
        topdirs =  ~/docs /usr/share/doc
        [~/somedirectory-with-utf8-txt-files]
        defaultcharset = utf-8
        
        There are three kinds of lines:
Comment (starts with #) or empty.
Parameter affectation (name = value).
Section definition ([somedirname]).
Depending on the type of configuration file, section definitions either separate groups of parameters or allow redefining some parameters for a directory sub-tree. They stay in effect until another section definition, or the end of file, is encountered. Some of the parameters used for indexing are looked up hierarchically from the current directory location upwards. Not all parameters can be meaningfully redefined, this is specified for each in the next section.
When found at the beginning of a file path, the tilde character (~) is expanded to the name of the user's home directory, as a shell would do.
White space is used for separation inside lists. List elements with embedded spaces can be quoted using double-quotes.
Encoding issues. Most of the configuration parameters are plain ASCII. Two particular sets of values may cause encoding issues:
File path parameters may contain non-ascii characters and should use the exact same byte values as found in the file system directory. Usually, this means that the configuration file should use the system default locale encoding.
The unac_except_trans
              parameter should be encoded in UTF-8. If your system
              locale is not UTF-8, and you need to also specify
              non-ascii file paths, this poses a difficulty because
              common text editors cannot handle multiple encodings
              in a single file. In this relatively unlikely case,
              you can edit the configuration file as two separate
              text files with appropriate encodings, and
              concatenate them to create the complete
              configuration.
RECOLL_CONFDIRDefines the main configuration directory.
RECOLL_TMPDIR, TMPDIRLocations for temporary files, in this order of
                priority. The default if none of these is set is to
                use /tmp. Big
                temporary files may be created during indexing,
                mostly for decompressing, and also for processing,
                e.g. email attachments.
RECOLL_CONFTOP,
              RECOLL_CONFMIDAllow adding configuration directories with priorities below and above the user directory (see above the Configuration overview section for details).
RECOLL_EXTRA_DBS,
              RECOLL_ACTIVE_EXTRA_DBSHelp for setting up external indexes. See this paragraph for explanations.
RECOLL_DATADIRDefines replacement for the default location of
                Recoll data files, normally found in, e.g.,
                /usr/share/recoll).
RECOLL_FILTERSDIRDefines replacement for the default location of
                Recoll filters, normally found in, e.g.,
                /usr/share/recoll/filters).
ASPELL_PROGaspell program to
                use for creating the spelling dictionary. The
                result has to be compatible with the libaspell which Recoll is using.
VARNAMEBlabla
recoll.conf is the main
          configuration file. It defines things like what to index
          (top directories and things to ignore), and the default
          character set to use for document types which do not
          specify it internally.
The default configuration will index your home directory. If this is not appropriate, start recoll to create a blank configuration, click , and edit the configuration file before restarting the command. This will start the initial indexing, which may take some time.
Most of the following parameters can be changed from the Index Configuration menu in the recoll interface. Some can only be set by editing the configuration file.
topdirsSpecifies the list of directories or files to
                  index (recursively for directories). You can use
                  symbolic links as elements of this list. See the
                  followLinks option
                  about following symbolic links found under the
                  top elements (not followed by default).
skippedNamesA space-separated list of wilcard patterns for names of files or directories that should be completely ignored. The list defined in the default file is:
skippedNames = #* bin CVS  Cache cache* caughtspam  tmp .thumbnails .svn \
               *~ .beagle .git .hg .bzr loop.ps .xsession-errors \
               .recoll* xapiandb recollrc recoll.conf 
                  The list can be redefined at any sub-directory in the indexed area.
The top-level directories are not affected by
                  this list (that is, a directory in topdirs might match and would
                  still be indexed).
The list in the default configuration does not
                  exclude hidden directories (names beginning with
                  a dot), which means that it may index quite a few
                  things that you do not want. On the other hand,
                  email user agents like thunderbird usually store
                  messages in hidden directories, and you probably
                  want this indexed. One possible solution is to
                  have .* in
                  skippedNames, and
                  add things like ~/.thunderbird or ~/.evolution in topdirs.
Not even the file names are indexed for
                  patterns in this list. See the noContentSuffixes variable for
                  an alternative approach which indexes the file
                  names.
noContentSuffixesThis is a list of file name endings (not wildcard expressions, nor dot-delimited suffixes). Only the names of matching files will be indexed (no attempt at MIME type identification, no decompression, no content indexing). This can be redefined for subdirectories, and edited from the GUI. The default value is:
noContentSuffixes = .md5 .map \
       .o .lib .dll .a .sys .exe .com \
       .mpp .mpt .vsd \
           .img .img.gz .img.bz2 .img.xz .image .image.gz .image.bz2 .image.xz \
       .dat .bak .rdf .log.gz .log .db .msf .pid \
       ,v ~ #
                skippedPaths and daemSkippedPathsA space-separated list of patterns for paths of files or directories that should be skipped. There is no default in the sample configuration file, but the code always adds the configuration and database directories in there.
skippedPaths is
                  used both by batch and real time indexing.
                  daemSkippedPaths can
                  be used to specify things that should be indexed
                  at startup, but not monitored.
Example of use for skipping text files only in a specific directory:
skippedPaths = ~/somedir/*.txt
              
                skippedPathsFnmPathnameThe values in the *skippedPaths variables are
                  matched by default with fnmatch(3), with the
                  FNM_PATHNAME flag. This means that '/' characters
                  must be matched explicitely. You can set
                  skippedPathsFnmPathname to 0 to
                  disable the use of FNM_PATHNAME (meaning that
                  /*/dir3 will match /dir1/dir2/dir3).
zipSkippedNamesA space-separated list of patterns for names of files or directories that should be ignored inside zip archives. This is used directly by the zip handler, and has a function similar to skippedNames, but works independantly. Can be redefined for filesystem subdirectories. For versions up to 1.19, you will need to update the Zip handler and install a supplementary Python module. The details are described on the Recoll wiki.
followLinksSpecifies if the indexer should follow
                  symbolic links while walking the file tree. The
                  default is to ignore symbolic links to avoid
                  multiple indexing of linked files. No effort is
                  made to avoid duplication when this option is set
                  to true. This option can be set individually for
                  each of the topdirs
                  members by using sections. It can not be changed
                  below the topdirs
                  level.
indexedmimetypesRecoll normally indexes any file which it knows how to read. This list lets you restrict the indexed MIME types to what you specify. If the variable is unspecified or the list empty (the default), all supported types are processed. Can be redefined for subdirectories.
excludedmimetypesThis list lets you exclude some MIME types from indexing. Can be redefined for subdirectories.
compressedfilemaxkbsSize limit for compressed (.gz or .bz2) files. These need to be decompressed in a temporary directory for identification, which can be very wasteful if 'uninteresting' big compressed files are present. Negative means no limit, 0 means no processing of any compressed file. Defaults to -1.
textfilemaxmbsMaximum size for text files. Very big text files are often uninteresting logs. Set to -1 to disable (default 20MB).
textfilepagekbsIf set to other than -1, text files will be indexed as multiple documents of the given page size. This may be useful if you do want to index very big text files as it will both reduce memory usage at index time and help with loading data to the preview window. A size of a few megabytes would seem reasonable (default: 1MB).
membermaxkbsThis defines the maximum size in kilobytes for an archive member (zip, tar or rar at the moment). Bigger entries will be skipped.
indexallfilenamesRecoll indexes file names in a special section of the database to allow specific file names searches using wild cards. This parameter decides if file name indexing is performed only for files with MIME types that would qualify them for full text indexing, or for all files inside the selected subtrees, independently of MIME type.
usesystemfilecommandDecide if we execute a system command
                  (file
                  -i by default) as a
                  final step for determining the MIME type for a
                  file (the main procedure uses suffix associations
                  as defined in the mimemap file). This can be
                  useful for files with suffix-less names, but it
                  will also cause the indexing of many bogus "text"
                  files.
systemfilecommandCommand to use for mime for mime type
                  determination if usesystefilecommand is set.
                  Recent versions of xdg-mime
                  sometimes work better than file.
processwebqueueIf this is set, process the directory where Web browser plugins copy visited pages for indexing.
webqueuedirThe path to the web indexing queue. This is
                  hard-coded in the Firefox plugin as ~/.recollweb/ToIndex so there
                  should be no need to change it.
Changing some of these parameters will imply a full reindex. Also, when using multiple indexes, it may not make sense to search indexes that don't share the values for these parameters, because they usually affect both search and index operations.
indexStripCharsDecide if we strip characters of diacritics
                  and convert them to lower-case before terms are
                  indexed. If we don't, searches sensitive to case
                  and diacritics can be performed, but the index
                  will be bigger, and some marginal weirdness may
                  sometimes occur. The default is a stripped index
                  (indexStripChars =
                  1) for now. When using multiple indexes
                  for a search, this parameter must be defined
                  identically for all. Changing the value implies
                  an index reset.
maxTermExpandMaximum expansion count for a single term (e.g.: when using wildcards). The default of 10000 is reasonable and will avoid queries that appear frozen while the engine is walking the term list.
maxXapianClausesMaximum number of elementary clauses we can add to a single Xapian query. In some cases, the result of term expansion can be multiplicative, and we want to avoid using excessive memory. The default of 100 000 should be both high enough in most cases and compatible with current typical hardware configurations.
nonumbersIf this set to true, no terms will be generated for numbers. For example "123", "1.5e6", 192.168.1.4, would not be indexed ("value123" would still be). Numbers are often quite interesting to search for, and this should probably not be set except for special situations, ie, scientific documents with huge amounts of numbers in them. This can only be set for a whole index, not for a subtree.
nocjkIf this set to true, specific east asian
                  (Chinese Korean Japanese) characters/word
                  splitting is turned off. This will save a small
                  amount of cpu if you have no CJK documents. If
                  your document base does include such text but you
                  are not interested in searching it, setting
                  nocjk may be a
                  significant time and space saver.
cjkngramlenThis lets you adjust the size of n-grams used for indexing CJK text. The default value of 2 is probably appropriate in most cases. A value of 3 would allow more precision and efficiency on longer words, but the index will be approximately twice as large.
indexstemminglanguagesA list of languages for which the stem
                  expansion databases will be built. See
                  recollindex(1) or
                  use the recollindex
                  -l command for
                  possible values. You can add a stem expansion
                  database for a different language by using
                  recollindex
                  -s, but it will be
                  deleted during the next indexing. Only languages
                  listed in the configuration file are
                  permanent.
defaultcharsetThe name of the character set used for files
                  that do not contain a character set definition
                  (ie: plain text files). This can be redefined for
                  any sub-directory. If it is not set at all, the
                  character set used is the one defined by the nls
                  environment ( LC_ALL,
                  LC_CTYPE, LANG), or iso8859-1 if nothing is set.
unac_except_transThis is a list of characters, encoded in
                  UTF-8, which should be handled specially when
                  converting text to unaccented lowercase. For
                  example, in Swedish, the letter a with diaeresis has full
                  alphabet citizenship and should not be turned
                  into an a. Each
                  element in the space-separated list has the
                  special character as first element and the
                  translation following. The handling of both the
                  lowercase and upper-case versions of a character
                  should be specified, as appartenance to the list
                  will turn-off both standard accent and case
                  processing. Example for Swedish:
unac_except_trans =  åå Åå ää Ää öö Öö
            
                  Note that the translation is not limited to a
                  single character, you could very well have
                  something like üue in the list.
The default value set for unac_except_trans can't be
                  listed here because I have trouble with SGML and
                  UTF-8, but it only contains ligature
                  decompositions: german ss, oe, ae, fi, fl.
This parameter can't be defined for subdirectories, it is global, because there is no way to do otherwise when querying. If you have document sets which would need different values, you will have to index and query them separately.
maildefcharsetThis can be used to define the default character set specifically for email messages which don't specify it. This is mainly useful for readpst (libpst) dumps, which are utf-8 but do not say so.
localfieldsThis allows setting fields for all documents
                  under a given directory. Typical usage would be
                  to set an "rclaptg" field, to be used in
                  mimeview to select
                  a specific viewer. If several fields are to be
                  set, they should be separated with a semi-colon
                  (';') character, which there is currently no way
                  to escape. Also note the initial semi-colon.
                  Example: localfields=
                  ;rclaptg=gnus;other = val, then select
                  specifier viewer with mimetype|tag=... in mimeview.
testmodifusemtimeIf true, use mtime instead of default ctime to determine if a file has been modified (in addition to size, which is always used). Setting this can reduce re-indexing on systems where extended attributes are modified (by some other application), but not indexed (changing extended attributes only affects ctime). Notes:
This may prevent detection of change in some marginal file rename cases (the target would need to have the same size and mtime).
You should probably also set noxattrfields to 1 in this case, except if you still prefer to perform xattr indexing, for example if the local file update pattern makes it of value (as in general, there is a risk for pure extended attributes updates without file modification to go undetected).
Perform a full index reset after changing the value of this parameter.
noxattrfieldsRecoll versions 1.19 and later automatically
                  translate file extended attributes into document
                  fields (to be processed according to the
                  parameters from the fields file). Setting this
                  variable to 1 will disable the behaviour.
metadatacmdsThis allows executing external commands for each file and storing the output in Recoll document fields. This could be used for example to index external tag data. The value is a list of field names and commands, don't forget an initial semi-colon. Example:
[/some/area/of/the/fs]
metadatacmds = ; tags = tmsu tags %f; otherfield = somecmd -xx %f
                
                  As a specially disgusting hack brought by
                  Recoll 1.19.7,
                  if a "field name" begins with rclmulti, the data returned by
                  the command is expected to contain multiple field
                  values, in configuration file format. This allows
                  setting several fields by executing a single
                  command. Example:
metadatacmds = ; rclmulti1 = somecmd %f
                
                  If somecmd
                  returns data in the form of:
field1 = value1
field2 = value for field2
                
                  field1 and
                  field2 will be set
                  inside the document metadata.
dbdirThe name of the Xapian data directory. It will be created if needed when the index is initialized. If this is not an absolute path, it will be interpreted relative to the configuration directory. The value can have embedded spaces but starting or trailing spaces will be trimmed. You cannot use quotes here.
idxstatusfileThe name of the scratch file where the indexer
                  process updates its status. Default: idxstatus.txt inside the
                  configuration directory.
maxfsoccuppcMaximum file system occupation before we stop indexing. The value is a percentage, corresponding to what the "Capacity" df output column shows. The default value is 0, meaning no checking.
mboxcachedirThe directory where mbox message offsets cache files are held. This is normally $RECOLL_CONFDIR/mboxcache, but it may be useful to share a directory between different configurations.
mboxcacheminmbsThe minimum mbox file size over which we cache the offsets. There is really no sense in caching offsets for small files. The default is 5 MB.
webcachedirThis is only used by the web browser plugin
                  indexing code, and defines where the cache for
                  visited pages will live. Default: $RECOLL_CONFDIR/webcache
webcachemaxmbsThis is only used by the web browser plugin indexing code, and defines the maximum size for the web page cache. Default: 40 MB. Quite unfortunately, this is only taken into account when creating the cache file. You need to delete the file for a change to be taken into account.
idxflushmbThreshold (megabytes of new text data) where we flush from memory to disk index. Setting this can help control memory usage. A value of 0 means no explicit flushing, letting Xapian use its own default, which is flushing every 10000 (or XAPIAN_FLUSH_THRESHOLD) documents, which gives little memory usage control, as memory usage also depends on average document size. The default value is 10, and it is probably a bit low. If your system usually has free memory, you can try higher values between 20 and 80. In my experience, values beyond 100 are always counterproductive.
The Recoll indexing process recollindex can use multiple threads to speed up indexing on multiprocessor systems. The work done to index files is divided in several stages and some of the stages can be executed by multiple threads. The stages are:
You can also read a longer document about the transformation of Recoll indexing to multithreading.
The threads configuration is controlled by two configuration file parameters.
thrQSizesThis variable defines the job input queues configuration. There are three possible queues for stages 2, 3 and 4, and this parameter should give the queue depth for each stage (three integer values). If a value of -1 is used for a given stage, no queue is used, and the thread will go on performing the next stage. In practise, deep queues have not been shown to increase performance. A value of 0 for the first queue tells Recoll to perform autoconfiguration (no need for the two other values in this case) - this is the default configuration.
thrTCountsThis defines the number of threads used for each stage. If a value of -1 is used for one of the queue depths, the corresponding thread count is ignored. It makes no sense to use a value other than 1 for the last stage because updating the Xapian index is necessarily single-threaded (and protected by a mutex).
The following example would use three queues (of depth 2), and 4 threads for converting source documents, 2 for processing their text, and one to update the index. This was tested to be the best configuration on the test system (quadri-processor with multiple disks).
thrQSizes = 2 2 2 thrTCounts = 4 2 1
The following example would use a single queue, and the complete processing for each document would be performed by a single thread (several documents will still be processed in parallel in most cases). The threads will use mutual exclusion when entering the index update stage. In practise the performance would be close to the precedent case in general, but worse in certain cases (e.g. a Zip archive would be performed purely sequentially), so the previous approach is preferred. YMMV... The 2 last values for thrTCounts are ignored.
thrQSizes = 2 -1 -1 thrTCounts = 6 1 1
The following example would disable multithreading. Indexing will be performed by a single thread.
thrQSizes = -1 -1 -1
autodiacsensIF the index is not stripped, decide if we
                  automatically trigger diacritics sensitivity if
                  the search term has accented characters (not in
                  unac_except_trans).
                  Else you need to use the query language and the
                  D modifier to
                  specify diacritics sensitivity. Default is
                  no.
autocasesensIF the index is not stripped, decide if we
                  automatically trigger character case sensitivity
                  if the search term has upper-case characters in
                  any but the first position. Else you need to use
                  the query language and the C modifier to specify
                  character-case sensitivity. Default is yes.
loglevel,daemloglevelVerbosity level for recoll and recollindex. A
                  value of 4 lists quite a lot of debug/information
                  messages. 2 only lists errors. The daemversion is specific to the
                  indexing monitor daemon.
logfilename,
                daemlogfilenameWhere the messages should go. 'stderr' can be
                  used as a special value, and is the default. The
                  daemversion is
                  specific to the indexing monitor daemon.
checkneedretryindexscriptThis defines the name for a command executed
                  by recollindex
                  when starting indexing. If the exit status of the
                  command is 0, recollindex
                  retries to index all files which previously could
                  not be indexed because of data extraction errors.
                  The default value is a script which checks if any
                  of the common bin
                  directories have changed (indicating that a
                  helper program may have been installed).
mondelaypatternsThis allows specify wildcard path patterns (processed with fnmatch(3) with 0 flag), to match files which change too often and for which a delay should be observed before re-indexing. This is a space-separated list, each entry being a pattern and a time in seconds, separated by a colon. You can use double quotes if a path entry contains white space. Example:
mondelaypatterns = *.log:20 "this one has spaces*:10"
              
                monixintervalMinimum interval (seconds) for processing the indexing queue. The real time monitor does not process each event when it comes in, but will wait this time for the queue to accumulate to diminish overhead and in order to aggregate multiple events to the same file. Default 30 S.
monauxintervalPeriod (in seconds) at which the real time monitor will regenerate the auxiliary databases (spelling, stemming) if needed. The default is one hour.
monioniceclass,
                monioniceclassdataThese allow defining the ionice class and data used by the indexer (default class 3, no data).
filtermaxsecondsMaximum handler execution time, after which it is aborted. Some postscript programs just loop...
filtermaxmbytesRecoll 1.20.7 and later. Maximum handler memory utilisation. This uses setrlimit(RLIMIT_AS) on most systems (total virtual memory space size limit). Some programs may start with 500 MBytes of mapped shared libraries, so take this into account when choosing a value. The default is a liberal 2000MB.
filtersdirA directory to search for the external input handler scripts used to index some types of files. The value should not be changed, except if you want to modify one of the default scripts. The value can be redefined for any sub-directory.
iconsdirThe name of the directory where recoll result list icons are stored. You can change this if you want different images.
idxabsmlenRecoll stores
                  an abstract for each indexed file inside the
                  database. The text can come from an actual
                  'abstract' section in the document or will just
                  be the beginning of the document. It is stored in
                  the index so that it can be displayed inside the
                  result lists without decoding the original file.
                  The idxabsmlen
                  parameter defines the size of the stored
                  abstract. The default value is 250 bytes. The
                  search interface gives you the choice to display
                  this stored text or a synthetic abstract built by
                  extracting text around the search terms. If you
                  always prefer the synthetic abstract, you can
                  reduce this value and save a little space.
idxmetastoredlenMaximum stored length for metadata fields. This does not affect indexing (the whole field is processed anyway), just the amount of data stored in the index for the purpose of displaying fields inside result lists or previews. The default value is 150 bytes which may be too low if you have custom fields.
aspellLanguageLanguage definitions to use when creating the aspell dictionary. The value must match a set of aspell language definition files. You can type "aspell config" to see where these are installed (look for data-dir). The default if the variable is not set is to use your desktop national language environment to guess the value.
noaspellIf this is set, the aspell dictionary generation is turned off. Useful for cases where you don't need the functionality or when it is unusable because aspell crashes during dictionary generation.
mhmboxquirksThis allows definining location-related quirks
                  for the mailbox handler. Currently only the
                  tbird flag is
                  defined, and it should be set for directories
                  which hold Thunderbird data, as their
                  folder format is weird.
This file contains information about dynamic fields
          handling in Recoll. Some
          very basic fields have hard-wired behaviour, and, mostly,
          you should not change the original data inside the
          fields file. But you can
          create custom fields fitting your data and handle them
          just like they were native ones.
The fields file has
          several sections, which each define an aspect of fields
          processing. Quite often, you'll have to modify several
          sections to obtain the desired behaviour.
We will only give a short description here, you should refer to the comments inside the default file for more detailed information.
Field names should be lowercase alphabetic ASCII.
A field becomes indexed (searchable) by having a prefix defined in this section.
A field becomes stored (displayable inside results) by having its name listed in this section (typically with an empty value).
This section defines lists of synonyms for the
                canonical names used inside the [prefixes] and [stored] sections
This section also defines aliases for the canonic field names, with the difference that the substitution will only be used at query time, avoiding any possibility that the value would pick-up random metadata from documents.
Some input handlers may need specific
                configuration for handling fields. Only the email
                message handler currently has such a section (named
                [mail]). It allows
                indexing arbitrary email headers in addition to the
                ones indexed by default. Other such sections may
                appear in the future.
Here follows a small example of a personal
          fields file. This would
          extract a specific email header and use it as a
          searchable field, with data displayable inside result
          lists. (Side note: as the email handler does no decoding
          on the values, only plain ascii headers can be indexed,
          and only the first occurrence will be used for headers
          that occur several times).
[prefixes] # Index mailmytag contents (with the given prefix) mailmytag = XMTAG [stored] # Store mailmytag inside the document data record (so that it can be # displayed - as %(mailmytag) - in result lists). mailmytag = [queryaliases] filename = fn containerfilename = cfn [mail] # Extract the X-My-Tag mail header, and use it internally with the # mailmytag field name x-my-tag = mailmytag
Recoll versions 1.19 and later process user extended file attributes as documents fields by default.
Attributes are processed as fields of the same name,
            after removing the user
            prefix on Linux.
The [xattrtofields]
            section of the fields
            file allows specifying translations from extended
            attributes names to Recoll field names. An empty
            translation disables use of the corresponding attribute
            data.
mimemap specifies the
          file name extension to MIME type mappings.
For file names without an extension, or with an
          unknown one, the system's file -i command will be executed to determine
          the MIME type (this can be switched off inside the main
          configuration file).
The mappings can be specified on a per-subtree basis,
          which may be useful in some cases. Example: gaim logs have a .txt extension but should be handled
          specially, which is possible because they are usually all
          located in one place.
The recoll_noindex
          mimemap variable has been
          moved to recoll.conf and
          renamed to noContentSuffixes, while keeping the
          same function, as of Recoll version 1.21. For older
          Recoll versions, see the
          documentation for noContentSuffixes but use recoll_noindex in mimemap.
mimeconf specifies how
          the different MIME types are handled for indexing, and
          which icons are displayed in the recoll result
          lists.
Changing the parameters in the [index] section is probably not a good idea except if you are a Recoll developer.
The [icons] section allows you to change the icons
          which are displayed by recoll in the result
          lists (the values are the basenames of the png images
          inside the iconsdir
          directory (specified in recoll.conf).
mimeview specifies which
          programs are started when you click on an Open link in a result list. Ie: HTML is
          normally displayed using firefox, but you may prefer
          Konqueror, your
          openoffice.org program
          might be named oofice instead of
          openoffice
          etc.
Changes to this file can be done by direct editing, or through the recoll GUI preferences dialog.
If Use desktop preferences to
          choose document editor is checked in the
          Recoll GUI preferences,
          all mimeview entries will
          be ignored except the one labelled application/x-all (which is set to use
          xdg-open by
          default).
In this case, the xallexcepts top level variable defines a
          list of MIME type exceptions which will be processed
          according to the local entries instead of being passed to
          the desktop. This is so that specific Recoll options such as a page number
          or a search string can be passed to applications that
          support them, such as the evince viewer.
As for the other configuration files, the normal usage
          is to have a mimeview
          inside your own configuration directory, with just the
          non-default entries, which will override those from the
          central configuration file.
All viewer definition entries must be placed under a
          [view] section.
The keys in the file are normally MIME types. You can
          add an application tag to specialize the choice for an
          area of the filesystem (using a localfields specification in
          mimeconf). The syntax for
          the key is mimetype|tag
The nouncompforviewmts
          entry, (placed at the top level, outside of the
          [view] section), holds a
          list of MIME types that should not be uncompressed before
          starting the viewer (if they are found compressed, ie:
          mydoc.doc.gz).
The right side of each assignment holds a command to be executed for opening the file. The following substitutions are performed:
%D. Document date
%f. File name. This may be the name of a temporary file if it was necessary to create one (ie: to extract a subdocument from a container).
%i. Internal path, for subdocuments of containers. The format depends on the container type. If this appears in the command line, Recoll will not create a temporary file to extract the subdocument, expecting the called application (possibly a script) to be able to handle it.
%M. MIME type
%p. Page index. Only significant for a subset of document types, currently only PDF, Postscript and DVI files. Can be used to start the editor at the right page for a match or snippet.
%s. Search term. The value will only be set for documents with indexed page numbers (ie: PDF). The value will be one of the matched search terms. It would allow pre-setting the value in the "Find" entry inside Evince for example, for easy highlighting of the term.
%u. Url.
In addition to the predefined values above, all
          strings like %(fieldname)
          will be replaced by the value of the field named
          fieldname for the document.
          This could be used in combination with field
          customisation to help with opening the document.
ptrans specifies
          query-time path translations. These can be useful in
          multiple cases.
The file has a section for any index which needs translations, either the main one or additional query indexes. The sections are named with the Xapian index directory names. No slash character should exist at the end of the paths (all comparisons are textual). An exemple should make things sufficiently clear
          [/home/me/.recoll/xapiandb]
          /this/directory/moved = /to/this/place
          [/path/to/additional/xapiandb]
          /server/volume1/docdir = /net/server/volume1/docdir
          /server/volume2/docdir = /net/server/volume2/docdir
        
        Imagine that you have some kind of file which does
            not have indexable content, but for which you would
            like to have a functional Open link in the result list (when
            found by file name). The file names end in .blob and can be
            displayed by application blobviewer.
You need two entries in the configuration files for this to work:
In $RECOLL_CONFDIR/mimemap
                  (typically ~/.recoll/mimemap), add the
                  following line:
.blob = application/x-blobapp
Note that the MIME type is made up here, and
                  you could call it diesel/oil just
                  the same.
In $RECOLL_CONFDIR/mimeview under
                  the [view] section,
                  add:
application/x-blobapp = blobviewer %f
We are supposing that blobviewer wants
                  a file name parameter here, you would use
                  %u if it liked URLs
                  better.
If you just wanted to change the application used by
            Recoll to display a
            MIME type which it already knows, you would just need
            to edit mimeview. The
            entries you add in your personal file override those in
            the central configuration, which you do not need to
            alter. mimeview can also
            be modified from the Gui.
Let us now imagine that the above .blob files actually
            contain indexable text and that you know how to extract
            it with a command line program. Getting Recoll to index the files is easy.
            You need to perform the above alteration, and also to
            add data to the mimeconf
            file (typically in ~/.recoll/mimeconf):
Under the [index]
                  section, add the following line (more about the
                  rclblob
                  indexing script later):
application/x-blobapp = exec rclblob
Under the [icons]
                  section, you should choose an icon to be
                  displayed for the files inside the result lists.
                  Icons are normally 64x64 pixels PNG files which
                  live in /usr/[local/]share/recoll/images.
Under the [categories] section, you should
                  add the MIME type where it makes sense (you can
                  also create a category). Categories may be used
                  for filtering in advanced search.
The rclblob handler should
            be an executable program or script which exists inside
            /usr/[local/]share/recoll/filters. It
            will be given a file name as argument and should output
            the text or html contents on the standard output.
The filter programming section describes in more detail how to write an input handler.