dconf(7)

NAME

   dconf - A configuration systen

DESCRIPTION

   dconf is a simple key/value storage system that is heavily optimised
   for reading. This makes it an ideal system for storing user preferences
   (which are read 1000s of times for each time the user changes one). It
   was created with this usecase in mind.

   All preferences are stored in a single large binary file. Layering of
   preferences is possible using multiple files (ie: for site defaults).
   Lock-down is also supported. The binary file for the defaults can
   optionally be compiled from a set of plain text keyfiles.

   dconf has a partial client/server architecture. It uses D-Bus. The
   server is only involved in writes (and is not activated in the user
   session until the user modifies a preference). The service is stateless
   and can exit freely at any time (and is therefore robust against
   crashes). The list of paths that each process is watching is stored
   within the D-Bus daemon itself (as D-Bus signal match rules).

   Reads are performed by direct access (via mmap) to the on-disk database
   which is essentially a hashtable. For this reason, dconf reads
   typically involve zero system calls and are comparable to a hashtable
   lookup in terms of speed. Practically speaking, in simple non-layered
   setups, dconf is less than 10 times slower than GHashTable.

   Writes are assumed only to happen in response to explicit user
   interaction (like clicking on a checkbox in a preferences dialog) and
   are therefore not optimised at all. On some file systems, dconf-service
   will call fsync() for every write, which can introduce a latency of up
   to 100ms. This latency is hidden by the client libraries through a
   clever "fast" mechanism that records the outstanding changes locally
   (so they can be read back immediately) until the service signals that a
   write has completed.

   The binary database format that dconf uses by default is not suitable
   for use on NFS, where mmap does not work well. To handle this common
   use case, dconf can be configured to place its binary database in
   XDG_RUNTIME_DIR (which is guaranteed to be local, but non-persistent)
   and synchronize it with a plain text keyfile in the users home
   directory.

PROFILES

   A profile is a list of configuration databases that dconf consults to
   find the value for a key. The user's personal database always takes the
   highest priority, followed by the system databases in the order
   prescribed by the profile.

   On startup, dconf consults the DCONF_PROFILE environment variable. If
   set, dconf will attempt to open the named profile, aborting if that
   fails. If the environment variable is not set, it will attempt to open
   the profile named "user" and if that fails, it will fall back to an
   internal hard-wired configuration. dconf stores its profiles in text
   files.  DCONF_PROFILE can specify a relative path to a file in
   /etc/dconf/profile/, or an absolute path (such as in a user's home
   directory). The profile name can only use alphanumeric characters or
   '_'.

   A profile file might look like the following:

       user-db:user
       system-db:local
       system-db:site

   Each line in a profile specifies one dconf database. The first line
   indicates the database used to write changes, and the remaining lines
   indicate read-only databases. (The first line should specify a user-db
   or service-db, so that users can actually make configuration changes.)

   A "user-db" line specifies a user database. These databases are found
   in $XDG_CONFIG_HOME/dconf/. The name of the file to open in that
   directory is exactly as it is written in the profile. This file is
   expected to be in the binary dconf database format. Note that
   XDG_CONFIG_HOME cannot be set/modified per terminal or session, because
   then the writer and reader would be working on different DBs (the
   writer is started by DBus and cannot see that variable).

   A "service-db" line instructs dconf to place the binary database file
   for the user database in XDG_RUNTIME_DIR. Since this location is not
   persistent, the rest of the line instructs dconf how to store the
   database persistently. A typical line is service-db:keyfile/user, which
   tells dconf to synchronize the binary database with a plain text
   keyfile in $XDG_CONFIG_HOME/dconf/user.txt. The synchronization is
   bi-directional.

   A "system-db" line specifies a system database. These databases are
   found in /etc/dconf/db/. Again, the name of the file to open in that
   directory is exactly as it is written in the profile and the file is
   expected to be in the dconf database format.

   If the DCONF_PROFILE environment variable is unset and the "user"
   profile can not be opened, then the effect is as if the profile was
   specified by this file:

       user-db:user

   That is, the user's personal database is consulted and there are no
   system settings.

KEY FILES

   To facilitate system configuration with a text editor, dconf can
   populate databases from plain text keyfiles. For any given system
   database, keyfiles can be placed into the /etc/dconf/db/database.d/
   directory. The keyfiles contain groups of settings as follows:

       # Some useful default settings for our site

       [system/proxy/http]
       host='172.16.0.1'
       enabled=true

       [org/gnome/desktop/background]
       picture-uri='file:///usr/local/rupert-corp/company-wallpaper.jpeg'

   After changing keyfiles, the database needs to be updated with the
   dconf(1) tool.

LOCKS

   System databases can contain 'locks' for keys. If a lock for a
   particular key or subpath is installed into a database then no database
   listed above that one in the profile will be able to modify any of the
   affected settings. This can be used to enforce mandatory settings.

   To add locks to a database, place text files in the
   /etc/dconf/db/database.d/locks directory, where database is the name of
   a system database, as specified in the profile. The files contain list
   of keys to lock, on per line. Lines starting with a # are ignored. Here
   is an example:

       # prevent changes to the company wallpaper
       /org/gnome/desktop/background/picture-uri

   After changing locks, the database needs to be updated with the
   dconf(1) tool.

PORTABILITY

   dconf mostly targets Free Software operating systems. It will
   theoretically run on Mac OS but there isn't much point to that (since
   Mac OS applications want to store preferences in plist files). It is
   not possible to use dconf on Windows because of the inability to rename
   over a file that's still in use (which is what the dconf-service does
   on every write).

API STABILITY

   The dconf API is not particularly friendly, and is not guaranteed to be
   stable. Because of this and the lack of portability, you almost
   certainly want to use some sort of wrapper API around it. The wrapper
   API used by GTK+ and GNOME applications is GSettings[1], which is
   included as part of GLib. GSettings has backends for Windows (using the
   registry) and Mac OS (using property lists) as well as its dconf
   backend and is the proper API to use for graphical applications.

SEE ALSO

   dconf-service(1), dconf-editor(1), dconf(1), GSettings[1]

NOTES

    1. GSettings
       http://developer.gnome.org/gio/stable/GSettings.html

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Free and Open Source Software