Provided by: elektra-doc_0.7.1-1_all 
NAME
elektra - A framework to store configuration atoms hierarchically Library Linkage Architecture.PP The
Elektra library (libelektra.so) has 2 layers: public methods and backend access, according to the
following architecture (these pictures were taken from the Elektra presentation[1]):
When using local backends such as the filesys backend, all key access happens in the actual process space
as bellow:
A remote daemon backend is also possible as noted bellow:
True Facts About Elektra
• It is much more an agreement then a piece of software. Relation is 99% to 1%.
• It is a simple and consistent API to help software developers programatically store and retrieve
global and user-specific configuration parameters.
• All key-value pairs are stored in clear-text files, UTF-8 encoded. All old charsets are also
supported, with automatic transparent conversion to and from UTF-8.
• API supports change notifications and multiple backends.
• It provides a unique namespace for all values. Anywhere, anytime, any program can preciselly access
keys by their names. Security restrictions may obviously apply.
• It is designed to be secure and lightweight, to let even early boot-stage programs like /sbin/init to
use it, instead of /etc/inittab file.
• It is designed to be easy to administrate with regular command line tools like cat, vi, cp, ls, ln.
Its storage is 100% open.
• It tries to set distribution-independent naming standards to store things like hardware
configuration, networking, user's session configuration, system's mime-types, parameters for kernel
modules, etc, that are generally stored under /etc.
• It requires existing software to be changed to use its API. This will substitute hundreds of
configuration-text-file parsing code, into clear Elektra's API key-value access methods.
• It is POSIX compliant. If it doesn't compile and run easily on some POSIX system, it should be easily
modified to do so.
Elektra Is Not
• Is NOT something that accesses SQL/relational databases.
• Is NOT an OS service that can become unavailable and make system unusable. It is just a library to
access files according to a namespace.
• Is NOT an alternative to network information systems like LDAP or NIS. These are still required for
networked environments.
• Is NOT a Webmin-like or other GUI tool to be used by end users.
• Is NOT an additional software layer to edit/generate existing configuration files.
• Is NOT a "configuration system", because one can't be created by simply writing some code. A
configuration system is an ecosystem, and the Elektra Project tries to help build one.
• It doesn't know a thing about the semantics of each data it stores.
Namespaces and Key Names.PP All keys are organized in a hierarchical tree with 2 Namespaces (subtrees) as
showed by the picture:
system
Contains all subsystems and global application keys/configuration. Equivalent to files under /etc
directory.
user
The current user's keys. Equivalent to the dotfiles in a user's $HOME directory. These keys are
phisically stored under the owner user home directory. The many user:username in the picture shows
the full name of those trees. Read about user domains bellow for more.
User Domains.PP Different from the system namespace, the user namespace is dynamic. For example, the key
user/env/PATH may have completely different values for users luciana and valeria. In this example, if
valeria wants to access this key at luciana's space, it should refer to user:luciana/env/PATH. Access
permissions apply.
User domains were implemented also to address situations when different user names ($USER) have same UID.
So a user key is stored in his home directory based on the user name, not the UID. Inactive Keys.PP A
great thing about text configuration files is that some configuration items can be there as an example,
but inactive or commented. Elektra provides a very simple way to simulate this behavior: if the key name
begins with a dot (.), it is considered inactive or commented. In real world applications, the Elektra
API will ignore these keys by default, but the keys are still accessible if the developer wants to.
These are some keys that have inactive subtrees:
• system/sw/XFree/InputDevice/.Mouse3/Driver: All keys under .Mouse3/* subtree won't be read by
default.
• user:valeria/env/env2/.PATH: The $PATH environment variable won't be set when valeria login.
• system/users/.louis/uid: The entire .louis/* subtree is inactive. This is the same as commenting the
user entry from a configuration file.
See bellow more examples of inactive keys. Key Examples.PP Here are some valid key names, and their
values:
The Elektra keys of the combined /etc/passwd and /etc/shadow entry for user 'nobody' would look like:
• system/users/nobody/uid: 99
• system/users/nobody/gid: 99
• system/users/nobody/gecos: Nobody
• system/users/nobody/home: /
• system/users/nobody/shell: /sbin/nologin
• system/users/nobody/password: *
• system/users/nobody/passwdChangeBefore: 0
• system/users/nobody/passwdChangeAfter: 99999
• system/users/nobody/passwdWarnBefore: 7
• system/users/nobody/passwdDisableAfter:
• system/users/nobody/passwdDisabledSince:
• system/users/nobody/passwdReserved:
The environment variables I want set, when I log in, with their full key name:
• user:aviram/env/env1/JAVA_HOME: /usr/lib/jvm/java-1.4.1-ibm-1.4.1.0/jre
• user:aviram/env/env2/PATH: $PATH:~/bin:$JAVA_HOME/bin
• user:aviram/env/env2/PS1: \h:\w\$
• user:aviram/env/env3/PILOTRATE: 57600
The entry in /etc/inittab that is responsible for starting X11 would look:
• system/init/x/runlevels: 5
• system/init/x/action: respawn
• system/init/x/process: /etc/X11/prefdm -nodaemon
The users database files and /etc/inittab were Elektrified to key-value pairs using the users-convert and
inittab-convert scripts included with the distribution.
An example of an elektrified /etc/X11/xorg.conf or /etc/X11/XF86Config:
• system/sw/xorg/current/Layouts/Default Layout/Inputs/Keyboard0/CoreKeyboard:
• system/sw/xorg/current/Layouts/Default Layout/Inputs/Mouse0/CorePointer:
• system/sw/xorg/current/Layouts/Default Layout/Screens/Screen0/Absolute.x: 0
• system/sw/xorg/current/Layouts/Default Layout/Screens/Screen0/Absolute.y: 0
• system/sw/xorg/current/Layouts/Default Layout/Screens/Screen0/ScreenNumber: 0
• system/sw/xorg/current/Files/FontPath: unix/:7100
• system/sw/xorg/current/Files/RgbPath: /usr/X11R6/lib/X11/rgb
• system/sw/xorg/current/Devices/Videocard0/BoardName: Intel 740 (generic)
• system/sw/xorg/current/Devices/Videocard0/Driver: i740
• system/sw/xorg/current/Devices/Videocard0/VendorName: Videocard vendor
• system/sw/xorg/current/InputDevices/Keyboard0/Driver: keyboard
• system/sw/xorg/current/InputDevices/Keyboard0/Options/XkbLayout: us_intl
• system/sw/xorg/current/InputDevices/Keyboard0/Options/XkbModel: pc105
• system/sw/xorg/current/InputDevices/Mouse0/Driver: mouse
• system/sw/xorg/current/InputDevices/Mouse0/Options/Device: /dev/input/mice
• system/sw/xorg/current/InputDevices/Mouse0/Options/Emulate3Buttons: yes
• system/sw/xorg/current/InputDevices/Mouse0/Options/Protocol: IMPS/2
• system/sw/xorg/current/InputDevices/Mouse0/Options/ZAxisMapping: 4 5
• system/sw/xorg/current/Monitors/Monitor0/DisplaySize.height: 230
• system/sw/xorg/current/Monitors/Monitor0/DisplaySize.width: 300
• system/sw/xorg/current/Monitors/Monitor0/HorizSync: 30.0 - 61.0
• system/sw/xorg/current/Monitors/Monitor0/ModelName: SyncMaster
• system/sw/xorg/current/Monitors/Monitor0/Options/dpms:
• system/sw/xorg/current/Monitors/Monitor0/VendorName: Monitor Vendor
• system/sw/xorg/current/Monitors/Monitor0/VertRefresh: 56.0 - 75.0
• system/sw/xorg/current/Monitors/.Monitor1/HorizSync: 30.0 - 61.0
• system/sw/xorg/current/Monitors/.Monitor1/ModelName: Impression
• system/sw/xorg/current/Monitors/.Monitor1/Options/dpms:
• system/sw/xorg/current/Monitors/.Monitor1/VendorName: Monitor Vendor
• system/sw/xorg/current/Monitors/.Monitor1/VertRefresh: 56.0 - 75.0
• system/sw/xorg/current/Screens/Screen0/DefaultDepth: 16
• system/sw/xorg/current/Screens/Screen0/Device: Videocard0
• system/sw/xorg/current/Screens/Screen0/Displays/00/Depth: 16
• system/sw/xorg/current/Screens/Screen0/Displays/00/Modes: 1024x768,800x600,640x480
• system/sw/xorg/current/Screens/Screen0/Displays/00/Viewport.x: 0
• system/sw/xorg/current/Screens/Screen0/Displays/00/Viewport.y: 0
• system/sw/xorg/current/Screens/Screen0/Monitor: Monitor0
• system/sw/xorg/current/Modules/dbe:
• system/sw/xorg/current/Modules/dri:
• system/sw/xorg/current/Modules/extmod:
• system/sw/xorg/current/Modules/fbdevhw:
• system/sw/xorg/current/Modules/freetype:
• system/sw/xorg/current/Modules/glx:
• system/sw/xorg/current/Modules/record:
• system/sw/xorg/current/Modules/type1:
• system/sw/xorg/current/DRI/Group: 0
• system/sw/xorg/current/DRI/Mode: 0666
Pay attention that the keys bellow system/sw/XFree/current/Monitor/.Monitor1 are inactive because we have
.Monitor1 as their parent. So unless special options are used when calling the API, these keys will not
be retrieved from the database.
Throughout this text you will see other examples of key names. Key Data Types.PP There are only two
types of data that can be stored:
Text
Handled as pure text. Regardeless of the charset being used, these values are always stored as UTF-8.
This ensures very strong internationalization and migration capabilities, while keeping simplicity.
If you don't want the Elektra framework to convert your non-ASCII text to UTF-8 (not recomended), you
should use the Binary data format.
Binary
A stream of bytes, not necessarily text. It is recommended that you avoid using binary values because
UNIX system administrators tend to consider them as unmanageable blackboxes. Anyway, the value will
be encoded into pure text format based on hexadecimal digits, for openness and ease of
administration. This data type should also be avoided because it is less efficient.
There are very good reasons why types like Integer, Time, Font, List, etc were not implemented: Elektra
was designed to be useful for any type of program, so having more specific data types implicates in the
definition of value limits, separators in the storage format, etc, that may be good for some application
and bad for other. So the semantics of the data is handled by the application. A program or framework may
define its own special data handling methods using these essential basic types. See the keyGetType() and
keySetType() methods documentation in the kdb(3) man page to understand how to set keys with your own
data types.
There are more two types of keys:
Directory
It can't store a value, but, as a directory in a filesystem, it serves as a way to group correlated
keys.
Link
It is a link to another key. They work as symbolic links in the filesystem: when trying to access
them, you will actually access the key they point to. The API also provides ways to access these
special keys without dereferencing them.
Key Meta Data.PP Besides the key name and the value, each key has other attributes:
Owner's User and Group
This is a system's UID and GID equal to the ones found in regular files' attributes.
Access Permissions
Filesystem-like access permissions for user, group and others.
Modification, Access and Stat Times
Last time a key was modified, readed and stated (listed), respectively.
Key Comment
Pretty much as a configuration file comment. Not intended to be used in GUI applications, because it
isn't internationalizable.
Fine Grained Security Example.PP To show this metadata in action, this screen shows the kdb command
listing keys and their attributes related to user nobody.
bash$ kdb ls -Rlv system/users/nobody
-rw-r--r-- root root 17 Mar 31 09:07 system/users/nobody/uid=99
-rw-r--r-- root root 17 Mar 31 09:07 system/users/nobody/gid=99
-rw-r--r-- root root 21 Mar 31 09:07 system/users/nobody/gecos=Nobody
-rw-r--r-- root root 16 Mar 31 09:07 system/users/nobody/home=/
-rw-r--r-- root root 28 Mar 31 09:07 system/users/nobody/shell=/sbin/nologin
-rw------- root root 16 Mar 31 09:07 system/users/nobody/password
-rw------- root root 16 Mar 31 09:07 system/users/nobody/passwdChangeBefore
-rw------- root root 20 Mar 31 09:07 system/users/nobody/passwdChangeAfter
-rw------- root root 16 Mar 31 09:07 system/users/nobody/passwdWarnBefore
-rw------- root root 15 Mar 31 09:07 system/users/nobody/passwdDisableAfter
-rw------- root root 15 Mar 31 09:07 system/users/nobody/passwdDisabledSince
-rw------- root root 15 Mar 31 09:07 system/users/nobody/passwdReserved
We ran the kdb command without super-user credentials, asking for long (-l), recursive (-R) listing, and
to show each key value (-v). But (since we are) regular user, we don't have permission to see the values
of the system/users/nobody/passwd* fields.
The users database files were elektrified to key-value pairs using the users-convert script included with
the distribution. ExamplesSetting Keys.PP bash$kdb set -c "My first key" user/example/key "Some nice
value"
bash$kdb set user:luciana/example/key -- "Some - nice - value with dashes"
bash#KDB_ROOT=user:http/sw/httpd kdb set -u nobody -g http key "Some value"
bash$kdb set -b image.png -t bin user/example/binaryKey
bash$kdb set -b file.txt user/example/regularKey
bash#kdb set -t link system/sw/XFree/current system/sw/XFree/handmade Getting Keys.PP
bash$KDB_ROOT=user/example kdb get some/key/name
bash$eval `kdb get -s user/env/env1/PS1`
bash$KDB_BACKEND=gconf kdb get user/sw/gnome-terminal/global/active_encodings Listing.PP bash$kdb ls -laR
user:valeria
bash$kdb ls -lR system/sw/xorg/current
bash$KDB_ROOT=system/sw kdb ls -lR xorg
bash$KDB_BACKEND=fstab kdb ls -Rv system/filesystems
bash$eval `kdb ls -Rvs user/env/env2` Miscelaneous.PP bash#kdb ln system/sw/xorg/handmade
system/sw/xorg/current
bash#kdb mv system/sw/xorg/current system/sw/xorg/old
bash#kdb rm system/inittab/rc4
bash$KDB_BACKEND=gconf kdb rm user/gconfKey XML Import and Export.PP bash#kdb export user/sw/app | sed -e
's|/app/|/app2/|g' | kdb import
bash#KDB_ROOT=system/sw kdb export myapp > myappconf.xml
bash#kdb import myappconf.xml
bash$KDB_BACKEND=gconf kdb export user/sw
SEE ALSO
kdb(1), elektra(5)
AUTHOR
Avi Alkalay <avi at unix.sh>
Linux Market Developer, Senior IT and Software Architect, IBM Linux Impact Team :: ibm.com/linux
Author.
COPYRIGHT
Copyright © 2004 Avi Alkalay
NOTES
1. Elektra presentation
[set $man.base.url.for.relative.links]/elektra.sxi
Elektra Initiative March 2004 ELEKTRA(7)