Ubuntu – Is it possible to monitor dconf for changes

The command-line tool dconf seems to show only those settings which are actually set in the database (so they are different from the default), whereas dconf-editor shows all possible settings. You will notice that the button "Set to Default" in dconf-editor is greyed out for those settings which are not shown by dconf.

• dconf-editor uses schema path to show settings data tree. Same structure used to store data in GVariant database.

• gsettings (from glib-2.0) uses schema id to show/get settings data. Same way as any other application should do which uses GSetttings API.

• It's up to the application developer to set both as he/she would like. (with some restriction for canonical naming). So path could be different than id but most application developers prefer to use identical word series/combination. Some don't preserve same capitalization. Example Tracker project from Gnome

  <schema id="org.freedesktop.Tracker.Miner" path="/org/freedesktop/tracker/miner/" />
  

  In addition to that, some alternative applications share same settings which belong to the Gnome desktop. Example: input-sources

• First, Apps should not mess with dconf

  Introduction from dconf project page:

  dconf is a low-level configuration system. Its main purpose is to provide a backend to GSettings on platforms that don't already have configuration storage systems.

• Where's the data stored? (Ref: https://wiki.gnome.org/Projects/dconf/SystemAdministrators)

  A profile is a list of configuration databases. What it seems that Gnome & Unity use same profile.

  $ cat /etc/dconf/profile/gdm
  user-db:user
  system-db:gdm
  

  1. user-db:user: First database in the profile is read-write rw and it is created in the user's home directory.

     $ file ~/.config/dconf/user
     /home/sneetsher/.config/dconf/user: GVariant Database file, version 0
     

  2. system-db:gdm: read-only

     $ file /etc/dconf/db/gdm
     /etc/dconf/db/gdm: GVariant Database file, version 0
     

     dconf could bind a text style store in addition to GVariant Database from db.d/* folder. Example (Notice file path, so it is a part of system-db:gdm):

      $ cat /etc/dconf/db/gdm.d/00-upstream-settings
     
      # This file is part of the GDM packaging and should not be changed.
      #
      # Instead create your own file next to it with a higher numbered prefix,
      # and run
      #
      #       dconf update
      #
     
      [org/gnome/desktop/a11y/keyboard]
      enable=true
     
      [org/gnome/desktop/background]
      show-desktop-icons=false
      ...
     

• Schema Files: Relation between schema id & schema path (*.gschema.xml)

  What is the schema XML file in the data/glib-2.0 folder of my Quickly application? by trent shows a nice example of using GSettings API in a Quickly application, and his conclusion based on his experience.

  Back to Vino. Each application that uses GSsettings should define its schema's and should store/install them in /usr/share/glib-2.0/schemas/ (It's a glib directory):

  $ dpkg -L vino | grep -i glib-2.0
  /usr/share/glib-2.0
  /usr/share/glib-2.0/schemas
  /usr/share/glib-2.0/schemas/org.gnome.Vino.enums.xml
  /usr/share/glib-2.0/schemas/org.gnome.Vino.gschema.xml
  
  $ more /usr/share/glib-2.0/schemas/org.gnome.Vino.gschema.xml
  <schemalist>
    <schema id='org.gnome.Vino' path='/org/gnome/desktop/remote-access/'>
      <key name='enabled' type='b'>
        <summary>Enable remote access to the desktop</summary>
        <description>
          If true, allows remote access to the desktop via the RFB
          protocol. Users on remote machines may then connect to the
          desktop using a VNC viewer.
        </description>
        <default>false</default>
      </key>
  
      <key name='prompt-enabled' type='b'>
        <summary>Prompt the user before completing a connection</summary>
        <description>
          If true, remote users accessing the desktop are not allowed
          access until the user on the host machine approves the
          connection. Recommended especially when access is not password
          protected.
        </description>
        <default>true</default>
      </key>
  ...
  

  If you noticed, The schema is defined with an id and a path. The schema file name follows the id value.

  <schema id='org.gnome.Vino' path='/org/gnome/desktop/remote-access/'>
  

• *.enums.xml files are for custom enumeration declaration, to be used as new data types in *.gschema.xml with same schema id.

  $ cat /usr/share/glib-2.0/schemas/org.gnome.Vino.enums.xml
  <!-- Generated data (by glib-mkenums) -->
  
  <schemalist>
    <enum id='org.gnome.Vino.VinoIconVisibility'>
      <value nick='never' value='0'/>
      <value nick='always' value='1'/>
      <value nick='client' value='2'/>
    </enum>
  </schemalist>
  
  <!-- Generated data ends here -->
  
  $ gsettings range org.gnome.Vino icon-visibility
  enum
  'never'
  'always'
  'client'
  
  $ gsettings get org.gnome.Vino icon-visibility
  'client'
  

• Compiling Schema's (Ref: Playing with dconf and gnome-tweak-tool)

  As part of the installation process (it has a dpkg trigger), schema's are compiled with glib-compile-schemas tool (from glib)

  sudo glib-compile-schemas /usr/share/glib-2.0/schemas
  

  *.gschema.xml will be compiled to a binary file /usr/share/glib-2.0/schemas/gschemas.compiled

• Vendor Override Files (*.gschema.override)

  In addition to schema files, glib-compile-schemas reads vendor override files, which are key files that can override default values for keys in the schemas (Ref: man glib-compile-schemas). They contain the changes done by Ubuntu distribution to override upstream schema defaults.

  $ ls /usr/share/glib-2.0/schemas/*.gschema.override
  /usr/share/glib-2.0/schemas/10_compiz-gnome.gschema.override
  /usr/share/glib-2.0/schemas/10_desktop-base.gschema.override
  /usr/share/glib-2.0/schemas/10_evolution-common.gschema.override
  /usr/share/glib-2.0/schemas/10_gnome-settings-daemon.gschema.override
  /usr/share/glib-2.0/schemas/10_gnome-shell.gschema.override
  /usr/share/glib-2.0/schemas/10_gnome-system-log.gschema.override
  /usr/share/glib-2.0/schemas/10_gsettings-desktop-schemas.gschema.override
  /usr/share/glib-2.0/schemas/10_libgtk-3-common.gschema.override
  /usr/share/glib-2.0/schemas/10_ubuntu-settings.gschema.override
  /usr/share/glib-2.0/schemas/20_ubuntu-gnome-default-settings.gschema.override
  
  $ cat /usr/share/glib-2.0/schemas/10_gnome-settings-daemon.gschema.override
  [org.gnome.desktop.wm.keybindings]
  switch-input-source=['<Super>space']
  switch-input-source-backward=['<Shift><Super>space']
  

  Example of override files use, See How to customize the Ubuntu Live CD? (5. Customization 2: Backgrounds and Themes).

• Lock files

  Currently, dconf supports only per-key locking, no sub-path lock. User defined values will still be stored in user-db but will have no effect on applications. dconf/gsettings returns default values instead for those locked keys. Lock files are stored in db.d/locks/. Example:

  $ cat /etc/dconf/db/gdm.d/locks/00-upstream-settings-locks 
  /org/gnome/desktop/a11y/keyboard/enable
  /org/gnome/desktop/background/show-desktop-icons
  /org/gnome/desktop/lockdown/disable-application-handlers
  /org/gnome/desktop/lockdown/disable-command-line
  /org/gnome/desktop/lockdown/disable-lock-screen
  /org/gnome/desktop/lockdown/disable-log-out
  /org/gnome/desktop/lockdown/disable-printing
  /org/gnome/desktop/lockdown/disable-print-setup
  /org/gnome/desktop/lockdown/disable-save-to-disk
  /org/gnome/desktop/lockdown/disable-user-switching
  ...
  

  After locks modification, to be effective run:

  sudo dconf update
  

  A good showcase: dconf Settings: defaults and locks

• Changing Global Settings

  The default for gsettings/dconf-editor is to edit the user-db. To change system-db, write a new override file and recompile schema's.

  I couldn't get this to work:

  sudo su gdm -c 'gsettings ...'
  

  neither the other answers here Set Default/Global Gnome Preferences (Gnome 3), may be that was for an old release.