KConfig

KConfig Entry Options

KConfig provides various options that can alter how it interprets configuration entries on a per-entry, per-group or per-file basis. Note that these are not supported by other configuration frameworks, and so should not be used in files that are intended to be used by applications that do not use KConfig (such as application desktop files).

Immutable Entries

KConfig's cascading configuration mechanism usually causes values from earlier, "global" configuration files to be overridden by later, "local" ones. Typically, the system administrator might set global defaults, and a user might override them in their local configuration files.

However, KConfig provides a way to lock down configuration values, so that the global settings override the local ones. This allows system administrators to restrict the values a user can set for an entry, group of entries or an entire configuration file.

This is important for Kiosk authorization (see the KAuthorized namespace), which allows parts of the user interface to be locked down.

Configuration entries can be marked as immutable with the $i option. This can be done on a per-entry basis:

[MyGroup]
someKey[$i]=42

on a per-group basis (which will prevent any attempts to modify entries in the group at all in later files):

[MyGroup][$i]
someKey=42

or for an entire file by putting [$i] at the start of the file:

[$i]
[MyGroup]
someKey=42
[MyOtherGroup]
someOtherKey=11

Once this is done, the immutable entries or groups cannot be overridden by later files of the same name (and, if the file is immutable, later files will be ignored entirely).

Note that a similar effect to file immutability can be achieved by using file system permissions to prevent the user from writing to their local versions of the configuration file, although (since this is normally a setup error), the user will be warned that the configuration file is not writable. This warning can be suppressed by adding the following setting to either the relevant configuration file or the kdeglobals file:

[General]
warn_unwritable_config=true

However, using file system permissions like this can potentially be circumvented by the user if they have write access to the containing directory or can modify environment variables (and XDG_CONFIG_HOME in particular).

Shell Expansion

If an entry is marked with $e, environment variables will be expanded.

Name[$e]=$USER

When the "Name" entry is read $USER will be replaced with the value of the $USER environment variable.

Note that the application will replace $USER with its expanded value after saving. To prevent this combine the $e option with $i (immmutable) option. For example:

Name[$ei]=$USER

This will make that the "Name" entry will always return the value of the $USER environment variable. The user will not be able to change this entry.

The following syntax for environment variables is also supported:

Name[$ei]=${USER}

There are three environment variables that have a fallback strategy if the environment variable is not set. They instead map to a location from QStandardPaths. They are:

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