Filesystem Hierarchy

 

Introduction

KDE defines a filesystem hierarchy which is used by the KDE environment itself as well as all KDE applications. In general KDE stores all it files in a fixed directory tree. By default there are two such directory trees, one at the system level and one at the user level in the user's home directory. However, as a system administrator you can create additional trees.

KDE and KDE applications look up files by scanning the directory trees. The directory trees are in order of precedence. When a file is present in multiple directory trees, the file from the first listed tree takes precendence. Normally, the tree located in the user's home directory has the highest precedence. This is also the directory tree where changes are written to.

For configuration files the story is slightly different. If there are multiple configuration files found in the directory trees with the same name their content is combined. The precedence order of the directory trees plays a role here. When two files define the same configuration key, the file with the highest precedence determines which value is used for the key.

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Location of the Directory Trees

The location of the KDE Directory Trees is determined by a number of environment variables. In KDE 2.x there were two environment variables. For KDE 3.x two more environment variables have been introduced. They are discussed below together with an explanation of what they can be used for.

Environment variables in KDE 2.x:

$KDEHOME

This environment variable determines the location of the user level directory tree and is used by KDE applications for creating and saving files. This directory tree has the highest precedence; files or settings found in this directory tree will take precendent over any files or settings found in other directory trees.

This directory tree is, as the name already suggests, normally located in the home directory of the user. If this environment variable is not defined the default location $HOME/.kde is used.

If the environment variable has a value that starts with a tilde (~), the tilde is replaced with the users home directory at runtime. In order to use this care must be taken to add proper quoting, otherwise the shell might do the expansion already resulting in undesired behaviour in combination with su.

$KDEDIR

This environment variable defines where the system level KDE directory tree is located. All data files such as icons, sound-files and menu description files that accompany applications are usually installed in this directory tree.

Additional environment variables in KDE 3.x:

$KDEROOTHOME

In order to prevent problems where applications that run as root save files with root-privileges in the user's home directory, the $KDEROOTHOME environment variable has been introduced in the KDE 3.x series. Applications that run with uid 0 (root) will use this variable to determine the location of the user level directory and where to save their files. If this variable is not defined the home directoy of the root user is looked up in the password file and .kde is appended. Usually that results in /root/.kde .

$KDEDIRS

Since KDE 3.x it is possible to specify more than a single system level directory tree. This makes it possible to let groups of users use a directory tree dedicated for their group. Such an additional directory tree can contain additional applications, specialized application resources or a specific set of default configurations suitable for the group. Specifying default configurations this way instead of using a /etc/skel construction has as advantage that changes in the default configuration can be made after the account of the user has been created.

The directories in $KDEDIRS should be seperated with a colon (:). The directories are listed in precedence order, the first directory has highest precedence, the last one lowest precedence. Since a group level directory tree should normally override any settings present at the system level, one would list the group level directory tree before the system level directory tree.

If $KDEDIRS is undefined, the single location specified by $KDEDIR is used instead.

In order to run KDE 2.x applications in a KDE 3.x environment one should point $KDEDIR to the location of the KDE 2.x installation and $KDEDIRS to the location of the KDE 3.x installation.

In general communication, references to the directory trees are made in terms of $KDEHOME to indicate the applicable user level directory tree, and in terms of $KDEDIR to indicate any of the system level directory trees.

Example

A staff member at a university could have the following settings:

KDEHOME='~/.kde3'
KDEROOTHOME='/root/.kde3'
KDEDIRS='/opt/kde_staff:/opt/kde3'

In this example the user settings are saved under the .kde3 directory in the user's home directory. Applications that run as root will save their settings to /root/.kde3 . KDE 3 has been installed to /opt/kde3 but there is also an additional directory tree located at /opt/kde_staff . Configuration files under that directory will take precedent over the ones in the /opt/kde3 system directories. /opt/kde-staff could contain additional applications that should only be available to staff members.

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Directory Tree

Each directory tree used by KDE has a fixed directory structure. Directories that are not relevant for a certain tree can be left out though. For example, directories used for temporary files are usually only found under $KDEHOME but not in any other directory tree.

The KDE runtime environment combines the sub-directories found under the various directory trees and refers to them as a single KDE resource. The KDE resource name is listed in the tables below.

There are three broad categories: files that are CPU/architecture specific, files that are host specific and files that are not specific with regards to host, CPU or architecture.

CPU/architecture specific directories:

Directory	KDE resource	Description
bin/	exe	Used for KDE executables.
cgi-bin/	cgi	CGI scipts that can be used by the KDE Help Center
lib/	lib	Used for KDE libraries.
lib/kde3/	module	This directory contains components, plugins and other runtime loadable objects for use by KDE 3.x applications.

The following are host specific directories. They are only available under $KDEHOME and are normally symlinked to locations outside the $KDEHOME directory tree.

Directory	KDE resource	Description
socket-<HOSTNAME>	socket	This directory contains communication sockets. The filesystem used by $KDEHOME may not be suitable for communication sockets. For that reason this directory is by default symlinked to another location.
tmp-<HOSTNAME>	tmp	This directory is used for temporary files. The filesystem used by $KDEHOME may be on a network. For performance reasons this directory is therefor by default symlinked to another location which is more likely to be on a local filesystem.
cache-<HOSTNAME>	cache	New in KDE 3.2. This directory is used for cached information such as HTTP objects, formatted help pages and the system configuration cache (ksycoca). Since this is non-essential information this directory is by default sylinked to a location outside $KDEHOME to help making backups of other information easier and to make it easier to reclaim diskspace.

The majority of directories involves data that is not CPU, architecture or host specific, all these directories are prefixed with share/ :

Directory	KDE resource	Description
share/applnk/	apps	Contains .desktop files describing the KDE-menu.
share/apps/	data	Contains applications specific data files. Each application has a sub-directory here for storing its files.
share/config/	config	Contains configuration files. Configuration files are normally named after the application they belong to followed by "rc". There are also files that are specific to a component and as such referenced by all applications that use that component. A special case is "kdeglobals", this file is read by all KDE applications.
share/config/session/	-	This directory is used by session management and is normally only available under $KDEHOME. At the end of a session KDE applications store their state here. The file names start with the name of the application followed by a number. The session manager "ksmserver" stores references to these numbers when saving a session in "ksmserverrc".
share/doc/HTML/	html	Documentation of KDE applications is stored here. Documentation is categorized by language and the application it belongs to. Normally at least two files can be found in a directory: "index.docbook" which contains the documentation in the unformatted docbook format and "index.cache.bz2" which contains the same documentation formatted as bzip2 compressed html. The html version is used by khelpcenter, if the html version is missing it will regenerate it from the docbook version but this is a time-consuming process.
share/icons/	icon	Under this directory icons are stored. Icons are categorized per theme, dimension and usage category.
share/mimelnk/	mime	In this directory .desktop files that describe mimetypes are stored.
share/services/	services	This directory contains .desktop files that describe services. Services and Applications are very similar, the major difference is that a Service is usually used by other Services or Applications while an Application is in general started by the user. Services do not appear in the KDE menu.
share/servicetypes/	servicetypes	This directory contains .desktop files that describe servicetypes. A servicetype usually represents a certain programming interface. Applications and Services include in their .desktop files the servicetypes that they provide.
share/sounds/	sound	This directory contains sound files.
share/templates/	templates	This dir contains templates for creating files of various types. A template consists of a .desktop file that describes the file and that includes a reference to a file in the .source sub-directory. The templates in this directory appearem in the "Create New" menu available on the desktop and in the file browser. When a user selects a template from the menu its source file is copied.
share/wallpapers/	wallpaper	This directory contains images that can be used as background picture.

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Outside the Directory Tree

As mentioned in the description of the Directory Tree, there are three host-specific directories that are usually symlinked to other locations. If the directories do not already exist, the following symlinks and directories will be created using the lnusertemp utility. Since both /tmp and /var/tmp are world writable, there is a possibility that one of the mentioned directories already exists but is owned by another user. In that case the lnusertemp utility will create a new directory with an alternative name and link to that instead.

Symlink	Description	Created with
$KDEHOME/socket-<HOSTNAME> --> /tmp/ksocket-<USER>/	Creates a directory for local communication sockets and point a symlink to it. The combined length of the directory name and the name of any communication socket should not exceed 106 characters. By default this directory is created under /tmp, other locations can be used by setting the KDETMP environment variable.	lnusertemp socket
$KDEHOME/tmp-<HOSTNAME> --> /tmp/kde-<USER>/	Creates a directory for temporary files and points a symlink to it. For performance reasons it is recommended to have this directory on a local filesystem but this is not strictly necassery. In KDE versions up to (and including) KDE 3.1, the system configuration cache (ksycoca and ksycocastamp) is located in here. It is recommended NOT to delete these files during boot since that will slow down the startup of KDE. By default this directory is created under /tmp, other locations can be used by setting the KDETMP environment variable.	lnusertemp tmp
$KDEHOME/cache-<HOSTNAME> --> /var/tmp/kdecache-<USER>/	New in KDE 3.2. Creates a directory for cache files and points a symlink to it. For performance reasons it is recommended to have this directory on a local filesystem but this is not strictly necassery. Since KDE 3.2, the system configuration cache (ksycoca and ksycocastamp) is located here. By default this directory is created under /var/tmp, other locations can be used by setting the KDEVARTMP environment variable.	lnusertemp cache

KDE uses two important files as part of its desktop communication protocol (DCOP) that are located outside the KDE directory trees. These are:

• $HOME/.ICEauthority - This file contains access tokens for DCOP. Applications must be able to provide an appropriate access token in order to communicate via DCOP and the dcopserver to other applications. When the dcopserver is started it will generate a new access token and stores it in this file. The $ICEAUTHORITY environment variable can be used to specify another file to be used instead.
• $HOME/.DCOPserver_$HOSTNAME_$DISPLAY - This file specifies how to access the dcopserver for a given host and a given X display. Since KDE 3.1.4 the $DCOPAUTHORITY environment variable can be used to specify another file to be used instead. Note that each concurrent KDE session must have its own unique file.

For kiosk setups it might sometimes be desirable to have the home-directory read-only. In that case $ICEAUTHORITY and $DCOPAUTHORITY should be pointed to writable locations. Normally KDE will abort when the home-directory is not writable. Since KDE 3.1.4 this can be prevented by setting the environment variable $KDE_HOME_READONLY to a non-empty value.

It has been reported that home directories mounted on some versions of Netware file systems do not support hardlinks. This causes problems with the generation of $HOME/.ICEauthority and results in KDE being unable to login. This situation can be remedied by setting the $ICEAUTHORITY variable to point to a file outside the home directory, for example somewhere under /tmp. Note that each user must have its own unqiue file.

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Adding Lookup Locations

KDE applications look up data files using the resource names listed in the Directory Tree section. The KDE runtime environment translates these names to actual directories. It does so by combining the locations of the directory trees with the directories listed in the tables.

Example

A user has the following directory tree settings:

KDEHOME='~/.kde3'
KDEDIRS='/opt/kde_staff:/opt/kde3'

When an application now looks for a "wallpaper" file, to each of the directory trees the directory "share/wallpapers/" is added. All of the resulting directories are then searched for the file:

~/.kde3/share/wallpapers/
/opt/kde_staff/share/wallpapers/
/opt/kde3/share/wallpapers/

By adding more directory tree to the KDEDIRS environment variable it is possible to expand the number of directories that are being searched. Sometimes it is desirable to include only a single directory in a search but not a whole directory tree. Additional directories can be configured in the kdeglobals configuration file in the "Directories" section. To do so assign one or more directories to the key "dir_" followed by the name of the resource. Multiple directories are seperated by a commas (,).

Example

To add the directory /data/photos to the wallpaper resource, put the following two lines in kdeglobals:

[Directories]
dir_wallpaper=/data/photos

When the application now looks for wallpaper files, it will look in the following locations:

/data/photos
~/.kde3/share/wallpapers/
/opt/kde_staff/share/wallpapers/
/opt/kde3/share/wallpapers/

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