1DCONF(7) Conventions and miscellaneous DCONF(7)
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6 dconf - A configuration system
7
9 dconf is a simple key/value storage system that is heavily optimised
10 for reading. This makes it an ideal system for storing user preferences
11 (which are read 1000s of times for each time the user changes one). It
12 was created with this usecase in mind.
13 All preferences are stored in a single large binary file. Layering of
15 preferences is possible using multiple files (ie: for site defaults).
16 Lock-down is also supported. The binary file for the defaults can
17 optionally be compiled from a set of plain text keyfiles.
18 dconf has a partial client/server architecture. It uses D-Bus. The
20 server is only involved in writes (and is not activated in the user
21 session until the user modifies a preference). The service is stateless
22 and can exit freely at any time (and is therefore robust against
23 crashes). The list of paths that each process is watching is stored
24 within the D-Bus daemon itself (as D-Bus signal match rules).
25 Reads are performed by direct access (via mmap) to the on-disk database
27 which is essentially a hashtable. For this reason, dconf reads
28 typically involve zero system calls and are comparable to a hashtable
29 lookup in terms of speed. Practically speaking, in simple non-layered
30 setups, dconf is less than 10 times slower than GHashTable.
31 Writes are assumed only to happen in response to explicit user
33 interaction (like clicking on a checkbox in a preferences dialog) and
34 are therefore not optimised at all. On some file systems, dconf-service
35 will call fsync() for every write, which can introduce a latency of up
36 to 100ms. This latency is hidden by the client libraries through a
37 clever "fast" mechanism that records the outstanding changes locally
38 (so they can be read back immediately) until the service signals that a
39 write has completed.
40 The binary database format that dconf uses by default is not suitable
42 for use on NFS, where mmap does not work well. To handle this common
43 use case, dconf can be configured to place its binary database in
44 XDG_RUNTIME_DIR (which is guaranteed to be local, but non-persistent)
45 and synchronize it with a plain text keyfile in the users home
46 directory.
47
49 A profile is a list of configuration databases that dconf consults to
50 find the value for a key. The user's personal database always takes the
51 highest priority, followed by the system databases in the order
52 prescribed by the profile.
53 On startup, dconf consults the DCONF_PROFILE environment variable. If
55 set, dconf will attempt to open the named profile, aborting if that
56 fails. If the environment variable is not set, it will attempt to open
57 the profile named "user" and if that fails, it will fall back to an
58 internal hard-wired configuration. dconf stores its profiles in text
59 files. DCONF_PROFILE can specify a relative path to a file in
60 /etc/dconf/profile/, or an absolute path (such as in a user's home
61 directory). The profile name can only use alphanumeric characters or
62 '_'.
63 A profile file might look like the following:
65 user-db:user
67 system-db:local
68 system-db:site
69 Each line in a profile specifies one dconf database. The first line
72 indicates the database used to write changes, and the remaining lines
73 indicate read-only databases. (The first line should specify a user-db
74 or service-db, so that users can actually make configuration changes.)
75 A "user-db" line specifies a user database. These databases are found
77 in $XDG_CONFIG_HOME/dconf/. The name of the file to open in that
78 directory is exactly as it is written in the profile. This file is
79 expected to be in the binary dconf database format. Note that
80 XDG_CONFIG_HOME cannot be set/modified per terminal or session, because
81 then the writer and reader would be working on different DBs (the
82 writer is started by DBus and cannot see that variable).
83 A "service-db" line instructs dconf to place the binary database file
85 for the user database in XDG_RUNTIME_DIR. Since this location is not
86 persistent, the rest of the line instructs dconf how to store the
87 database persistently. A typical line is service-db:keyfile/user, which
88 tells dconf to synchronize the binary database with a plain text
89 keyfile in $XDG_CONFIG_HOME/dconf/user.txt. The synchronization is
90 bi-directional.
91 A "system-db" line specifies a system database. These databases are
93 found in /etc/dconf/db/. Again, the name of the file to open in that
94 directory is exactly as it is written in the profile and the file is
95 expected to be in the dconf database format.
96 If the DCONF_PROFILE environment variable is unset and the "user"
98 profile can not be opened, then the effect is as if the profile was
99 specified by this file:
100 user-db:user
102 That is, the user's personal database is consulted and there are no
105 system settings.
106
108 To facilitate system configuration with a text editor, dconf can
109 populate databases from plain text keyfiles. For any given system
110 database, keyfiles can be placed into the /etc/dconf/db/database.d/
111 directory. The keyfiles contain groups of settings as follows:
112 # Some useful default settings for our site
114 [system/proxy/http]
116 host='172.16.0.1'
117 enabled=true
118 [org/gnome/desktop/background]
120 picture-uri='file:///usr/local/rupert-corp/company-wallpaper.jpeg'
121 After changing keyfiles, the database needs to be updated with the
124 dconf(1) tool.
125
127 System databases can contain 'locks' for keys. If a lock for a
128 particular key or subpath is installed into a database then no database
129 listed above that one in the profile will be able to modify any of the
130 affected settings. This can be used to enforce mandatory settings.
131 To add locks to a database, place text files in the
133 /etc/dconf/db/database.d/locks directory, where database is the name of
134 a system database, as specified in the profile. The files contain list
135 of keys to lock, on per line. Lines starting with a # are ignored. Here
136 is an example:
137 # prevent changes to the company wallpaper
139 /org/gnome/desktop/background/picture-uri
140 After changing locks, the database needs to be updated with the
143 dconf(1) tool.
144
146 dconf mostly targets Free Software operating systems. It will
147 theoretically run on Mac OS but there isn't much point to that (since
148 Mac OS applications want to store preferences in plist files). It is
149 not possible to use dconf on Windows because of the inability to rename
150 over a file that's still in use (which is what the dconf-service does
151 on every write).
152
154 The dconf API is not particularly friendly, and is not guaranteed to be
155 stable. Because of this and the lack of portability, you almost
156 certainly want to use some sort of wrapper API around it. The wrapper
157 API used by GTK+ and GNOME applications is GSettings[1], which is
158 included as part of GLib. GSettings has backends for Windows (using the
159 registry) and Mac OS (using property lists) as well as its dconf
160 backend and is the proper API to use for graphical applications.
161
163 dconf-service(1), dconf-editor(1), dconf(1), GSettings[1]
164
166 1. GSettings
167 http://developer.gnome.org/gio/stable/GSettings.html
168dconf DCONF(7)