Provided by: elektra-doc_0.7.1-1_all
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
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
· 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
· 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
· 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
· 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:
Contains all subsystems and global application keys/configuration.
Equivalent to files under /etc directory.
The current user's keys. Equivalent to the dotfiles in a user's
$HOME directory. These keys are phisically stored under the owner
user home directory. The many user:username in the picture shows
the full name of those trees. Read about user domains bellow for
User Domains.PP Different from the system namespace, the user namespace
is dynamic. For example, the key user/env/PATH may have completely
different values for users luciana and valeria. In this example, if
valeria wants to access this key at luciana's space, it should refer to
user:luciana/env/PATH. Access permissions apply.
User domains were implemented also to address situations when different
user names ($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
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
The environment variables I want set, when I log in, with their full
· 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
· 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
An example of an elektrified /etc/X11/xorg.conf or /etc/X11/XF86Config:
· 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
· system/sw/xorg/current/Devices/Videocard0/Driver: i740
· system/sw/xorg/current/Devices/Videocard0/VendorName: Videocard
· system/sw/xorg/current/InputDevices/Keyboard0/Driver: keyboard
· system/sw/xorg/current/InputDevices/Mouse0/Driver: mouse
· system/sw/xorg/current/InputDevices/Mouse0/Options/Protocol: IMPS/2
· system/sw/xorg/current/InputDevices/Mouse0/Options/ZAxisMapping: 4
· 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/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/VendorName: Monitor
· 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/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/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:
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
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:
It can't store a value, but, as a directory in a filesystem, it
serves as a way to group correlated keys.
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
Owner's User and Group
This is a system's UID and GID equal to the ones found in regular
Filesystem-like access permissions for user, group and others.
Modification, Access and Stat Times
Last time a key was modified, readed and stated (listed),
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$kdb set -c "My first key" user/example/key "Some nice
bash$kdb set user:luciana/example/key -- "Some - nice - value with
bash#KDB_ROOT=user:http/sw/httpd kdb set -u nobody -g http key "Some
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
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
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
Avi Alkalay <avi at unix.sh>
Linux Market Developer, Senior IT and Software Architect, IBM Linux
Impact Team :: ibm.com/linux
Copyright © 2004 Avi Alkalay
1. Elektra presentation