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man pages section 7: Standards, Environments, Macros, Character Sets, and Miscellany

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Updated: Thursday, June 13, 2019
 
 

dconf (7)

Name

dconf - A configuration systen

Synopsis

Please see following description for synopsis

Description

Conventions and miscellaneous                                         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.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+-----------------------+
       |ATTRIBUTE TYPE |   ATTRIBUTE VALUE     |
       +---------------+-----------------------+
       |Availability   | library/gnome/dconf   |
       +---------------+-----------------------+
       |Stability      | Pass-through volatile |
       +---------------+-----------------------+
SEE ALSO
       dconf-service(1), dconf-editor(1), dconf(1), GSettings[1]

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


       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from
       https://download.gnome.org/sources/dconf/0.26/dconf-0.26.0.tar.xz

       Further information about this software can be found on the open source
       community website at http://wiki.gnome.org/dconf.



dconf                                                                 DCONF(7)