NAME

       elektra-namespaces - namespaces

INTRODUCTION

       Every  key in Elektra has a unique name. Sometimes, multiple keys denote the same configuration item from
       different sources, e.g.:

       •   by a commandline argument

       •   by a configuration file found below the home directory

       •   by a configuration file found below /etc

       To allow such keys to exist in parallel, Elektra uses namespaces.

       A namespace has following properties:

       •   in-memory Keys can start with this name

       •   these keys stem from a specific configuration source

       •   ksLookup() uses namespaces in a specific default order unless specified otherwise

       Following parts of Elektra are affected by namespaces:

       •   the key name validation in keySetName()

       •   keyGetNamespace() which enumerates all namespaces

       •   _Backend and split.c for correct distribution to plugins (note that not all namespaces  actually  are
           distributed to configuration files)

       •   mount.c for cascading and root backends

       •   and of course many unit tests

       In the rest of this document all currently available namespaces in the default order are described.

spec

       Unlike the other namespaces, the specification namespace does not contain values of the keys, but instead
       meta data as described in [METADATA.ini].

       When  a  key  is looked up, keys from the spec-namespace are the first to be searched. When a spec-key is
       found, the rest of the lookup will be  done  as  specified,  probably  in  a  different  order  than  the
       namespaces enlisted here.

       Usually,  the  spec-keys do not directly contribute to the value, with one notable exception: the default
       value (meta data default, see in cascading below) might be used if every other way as  specified  in  the
       spec-key failed.

       Spec-keys  typically include a explanation and description for the key itself (but not comments which are
       specific for individual keys).

       The spec configuration files are below CMAKE_INSTALL_PREFIX/KDB_DB_SPEC.

       spec is not part of cascading mounts, because the specifications often are written  in  different  syntax
       than the configuration files.

proc

       Derived from the process (e.g. by parsing /proc/self or by arguments passed from the main method):

       •   program name

       •   arguments

       •   environment

       Keys  in  the  namespace  proc  can  not  be  stored  by  their nature. They might be different for every
       invocation of an application.

dir

       Keys from the namespace dir are  derived  from  a  directory  special  to  the  user  starting/using  the
       application, e.g.:

       •   the current working directory for project specific settings, e.g. .git

       •   the directory a server wants to present to the user, e.g. .htaccess

       Note  that Elektra only supports a single special directory per KDB instance. Start a new KDB instance if
       you need different special directories for different  parts  of  your  application.  How  to  change  the
       directory  may  be different dependent on the resolver, e.g. by using chdir or by setting the environment
       variable PWD

user

       On multi-user  operating  systems  obviously  every  user  wants  her/his  own  configuration.  The  user
       configuration is located in the users home directory typically below the folder KDB_DB_USER. Other pathes
       below the home directory are possible too (absolute path for resolver).

       Note  that  Elektra only supports a user directory per KDB instance. Start a new KDB instance if you need
       different user configuration for different parts of your application. How  to  change  the  user  may  be
       different dependent on the resolver, e.g. by seteuid() or by environment variables like HOME, USER

system

       The system configuration is the same for every chroot.

       The  configuration  is  typically  located  below KDB_DB_SYSTEM. Other absolut pathes, e.g. below /opt or
       /usr/local/etc are possible too.

cascading

       Keys that are not in a namespace (i.e. start with an /) are called cascading keys. Cascading keys do  not
       stem  from  a configuration source, but are used by applications to lookup a key in different namespaces.
       So, multiple keys can contribute to each cascading key name.

       Cascading is the same as a  name  resolution  and  provides  a  namespace  unification  as  described  in
       Versatility and Unix semantics in namespace unification http://dl.acm.org/citation.cfm?id=1138045.

       Keys  without  a namespace can not be stored by their nature. So they are transient: after a restart they
       are forgotten.

       Keys of that namespace are only used by ksLookup when no other suitable key was found. So they  have  the
       lowest possible priority, even fallback keys are preferred.

       Read more about cascading. /doc/help/elektra-cascading.md

                                                    July 2017                              ELEKTRA-NAMESPACES(7)