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       elektra - A framework to store configuration atoms hierarchically Library Linkage
       Architecture.PP The Elektra library ( 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:

           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

       ·   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-

       ·   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:

           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

           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 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

       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


       kdb(1), elektra(5)


       Avi Alkalay <avi at>
       Linux Market Developer, Senior IT and Software Architect, IBM Linux Impact Team ::


       Copyright © 2004 Avi Alkalay


        1. Elektra presentation
           [set $man.base.url.for.relative.links]/elektra.sxi