1DCONF(7) Conventions and miscellaneous DCONF(7)
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6 dconf - A configuration system
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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.
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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 rela