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KDE uses a simple text-based file format for all its configuration files. It consists of key-value pairs that are placed in groups. All KDE configuration files use UTF-8 encoding for text outside the ASCII range.
The start of a group is indicated by a group name that is placed in square brackets. All the key-value entries that follow belong to the group. The group ends when either another group starts or when the end of the file is reached.
Entries at the top of the file that are not preceded by a group name belong to the default group.
The following example shows a configuration file that consists of two groups.
The first group contains the keys "LargeCursor" and
"SingleClick", the second group contains the keys
"Show hidden files" and "Sort by".
[KFileDialog Settings] Show hidden files=false Sort by=Name
Entries in a group consists of a key and value separated by an equal sign. The key can contain spaces and may be followed by options placed in square brackets.
The part after the equal sign is the value of the entry. Any white space surrounding the equal sign is ignored, as is any trailing white space.
If a value is supposed to include a space at the begin or end then this can be achieved by using a backslash followed by an 's'.
There are several other backslash codes, here is the complete list:
The following config file fragment is equivalent to the one in the
previous example. Whitespace surrounding the key and value is ignored.
SingleClick = true
Show hidden files = false
Sort by =Name
In the following example the value of the "Caption" entry starts
with two spaces while the "Description" entry contains three lines
of text. Linefeeds in backslash notation are used to separate the different lines.
Caption=\s My Caption
Description=This is\na very long\ndescription.
Empty lines in configuration files are ignored, just as lines that start with a hash mark '#'. The hash mark can be used to add comments to configuration files but it should be noted that when a KDE application updates a configuration file the comments are not preserved.
There can be multiple configuration files with the same name in the share/config sub-directory of the various KDE Directory Trees. In that case the information of all these configuration files is combined on a key-by-key basis. If the same key within a certain group is defined in more than one place, the key value read from the directory tree with the highest precedence will be used. Configuration files under $KDEHOME always have the highest precedence. If a key in a certain group is defined multiple times in a single file, the value of the last entry is used.
KDE's cascading configuration scheme can be used to provide users with system or organisation-wide default settings while still allowing the users to make individual changes to these settings. KDE will not write entries to the user's configuration file under $KDEHOME that match any default settings provided this way. This way changes made to the default settings will immediately be propagated to the user. Note that differs from the traditional way of providing default settings for users through the use of /etc/skel, changes to /etc/skel will only be propagated when creating a new user account.
When it is undesirable that individual users can make changes to default settings, the default setting can be locked down.
So called Shell Expansion can be used to provide more dynamic default values. With shell expansion the value of a configuration key can be constructed from the value of an environment variable or from the output of a shell command.
To enable shell expansion for a configuration entry, the key must be followed by [$e]. Normally the expanded form is written into the users configuration file after first use. To prevent that, it is recommend to lock the configuration entry down by using [$ie].
In the following example the value for the "Host" entry is determined by the output of the hostname program. This setting is also locked down to ensure that the value is always determined dynamically.
The value for the "Email" entry is determined by filling in the values of the $USER and $HOST environment variables. When joe is logged in on joes_host this will result in a value equal to "joe@joes_host". The setting is not locked down.
All configuration entries can be indexed with a language code. In this case, the language that the user has selected for use on the desktop is used to look up the key value. If the default language (American English) has been selected or if there is no index that corresponds to the selected language, the key entry without index is used.
In the following example the value of the "Caption" entry
depends on the language. If the user has selected french as language (language
code fr) the value of the entry will be "Ma Légende".
In all other cases the value "My Caption" will be used.
To prevent users from overriding default settings, you can lock these settings down in the system-wide config files. Settings can be locked down individually, per group, or per file. An individual entry can be locked down by adding [$i] behind the key. A group of entries can be locked down by placing [$i] behind the group name. To lock down the entire file, start the file with [$i] on a single line.
In the following example the "Caption" entry has been locked
down. All entries in the "Mail Settings" group have been
locked down as well.
[Mail Settings][$i] Host[$e]=$(hostname) Emailemail@example.com
If an entry has been locked down, entries that would otherwise take precedence over the default setting will now be ignored.
Any changes that applications make to settings that have been locked down will be silently dropped. Applications may respond differently to locked down settings. Some applications recognize when a setting has been locked down and will remove the elements from its user interface. Other applications will continue to offer these options in their user interface even though the option does not have any effect any more. It is also possible that it is actually still possible to change the setting in the running program. In that case the changed setting will be effective for the time the program remains running. When the program is restarted it will then return to the locked-down default settings.
If you do not want to use a text editor then KConfigEditor offers a convenient way to edit KDE configuration files.
For scripts or modifying files from the command line, the command line app kwriteconfig is very useful. kwriteconfig expects a configuration file name, a group, a key, an optional type and a value, such as:
kwriteconfig --file kickerrc \
--group General \ --key AutoHidePanel \ --type bool \ true