Elektra
0.8.16
|
elektrify-getenv
<application> <options>
When an application is elektrified using libelektragetenv, it does not only request environ
, but also Elektra for every getenv(3) and secure_getenv(3) library call.
Its main purpose is to:
It is implemented using a LD_PRELOAD technique, see USAGE below for global activation.
The main purpose of this approach is to finally have a well-defined way to set and get environment variables. Elektra's variables will be in use immediately for every newly started application (no relogin necessary).
To do so, getenv(3) will lookup multiple sources next to searching in the environment (environ). As running example will use getenv("HOME") -> /path/to/home
:
Given commandline parameters will always be preferred (see OPTIONS below).
E.g. elektrify-getenv <app> --elektra:HOME=/path/to/home
Then /env/override/<key>
will be looked up, where <key> is the parameter to getenv
. If found, the key will be returned, if it is a null keys, getenv
will return NULL
.
E.g. kdb set user/env/override/HOME /path/to/home
Then environment will be requested.
E.g. HOME=/path/to/home elektrify-getenv <application>
Then /env/fallback/<key>
will be looked up. If found, the key will be returned, if it is a null keys, getenv
will return NULL
.
E.g. kdb set user/env/fallback/HOME /path/to/home
When elektrify-getenv
is active, every application additionally accepts Elektra's getenv options. Interleaving Elektra's and the application's options is allowed. Elektra will parse its options (starting with –elektra) first and discard them before the other application is started. Therefore the application will not see that they even existed, e.g.: given elektrify-getenv <application> -V --elektra-debug -L
the application will be called with <application> -V -L
.
--elektra-help
: Outputs this help.--elektra-version
: Gives version information.--elektra-debug=file
, ELEKTRA_DEBUG
or /env/option/debug
: Trace all getenv(3) calls to a file. stderr if no file is given, e.g. kdb set user/env/option/debug ""
. Note that null values (no forth argument), will disable debug messages. See examples below.--elektra-clearenv
, ELEKTRA_CLEARENV
or /env/option/clearenv
: Call clearenv(3) before entering main. This is a recommended security feature. Elektra itself, if configured that way, will still be able to use the environment.--elektra-reload-timeout=time_in_ms
, ELEKTRA_RELOAD_TIMEOUT
or /env/option/reload_timeout
: Activate a timeout based feature when a time is given in ms (and is not 0).Internal Options are available in three different variants:
--elektra-<option>
, which are not passed through exec(3) calls.ELEKTRA_<OPTION>
. which might be passed through exec(3) calls, but are removed by clearenv(3) calls.as Elektra KDB entry: /env/option/<option>
, which are the way to achieve an option to be enabled for every application.
E.g. kdb set user/env/option/clearenv ""
to clear the environment for all applications started by that user (note that at least PATH
should to be set using kdb set user/env/fallback/PATH "/bin:/usr/bin"
then).
Note, that null keys are equal to non-set options. E.g. kdb set system/env/option/debug "/tmp/elektra.log"
and kdb set user/env/option/debug
will activate logging for the system, except for the current user.
--elektra%<name>%=<value>
or /env/layer/<name>
: Add the contextual information (=layer) %<name>%
with its value <value>
. Note that name%
is predefined with argv[0]
and basename%
with basename(argv[0])
.Values can contain / to form hierarchies, e.g. --elektraname%=app/profile
--elektra:key=value
, /env/override/<key>
or /env/fallback/<key>
: set a key/value to be preferred, i.e. the first to considered as explained in LOOKUP.Keys can contain / to form hierarchies, e.g. --elektra:my/HOME=/path/to/home
.
To always use Elektra's getenv environment, simply add the output to the file:
elektrify-getenv | tail -1 | sudo tee -a /etc/ld.so.preload
this also can be done using Elektra:
sudo kdb mount /etc/ld.so.preload system/ld/preload line null sudo kdb set "system/ld/preload/new" `elektrify-getenv | tail -1`
The metadata context
in the specification can be used to facilitate a context-dependent lookup. In its metavalue all replacements of %<name>%
will be replaced by the given contextual options --elektra%<name>%=<value>
and /env/layer/<name>
keys.
E.g. to have a different home directory for any user and application:
kdb set user/env/layer/user markus kdb set user/users/markus/konqueror/HOME /home/download kdb setmeta spec/env/override/HOME context /users/%user%/%name%/HOME
Some applications do not use getenv(3)
or secure_getenv(3)
for requesting the environment, e.g. shells. This approach cannot work for them.
In the startup-phase (before main is even entered), getenv(3)
will not consider /env/override/
or /env/fallback
.
Elektra internally tries to avoid using the environment. Some resolvers, however, use it to conform to some specifications, e.g. XDG. Depending on the setup you use, these parameters might be used. For more information see:
kdb info resolver
For these parameters, /env/override/
or /env/fallback
will not be used internally, but will be used if applications request them, too.
If you use the standard resolvers, the bug won't have any effect.
Also note that --elektra-debug
or ELEKTRA_DEBUG
does not log getenv(3)
used by plugins during the startup-phase.
Command line arguments apply always to the outmost command, e.g. nice ls --elektra:COLUMNS=20
won't have any effect because only for nice
COLUMNS
will be set.
For illustration this section gives some more examples.
elektrify-getenv man man --elektra:MANWIDTH=40
Will use MANWIDTH 40 for this invocation of man man. This feature is handy, if an option is only available by environment, but not by command-line arguments, because sometimes environment variables are not trivial to set (e.g. in Makefiles).
Debugging:
# system wide to stderr (not recommended!): sudo kdb set system/env/option/debug "" # system wide to /var/log/elektra.log: sudo kdb set system/env/option/debug "/var/log/error.log" # but for my user to ~/.elektra.log: kdb set user/env/option/debug "$HOME/.elektra.log" # or disable it for my user: kdb set user/env/option/debug
Some more examples:
kdb set user/env/override/MANOPT -- "--regex -LC" elektrify-getenv getenv MANOPT # to check if it is set as expected kdb getenv MANOPT # if /etc/ld.so.preload is active
Will permanently and user-wide change MANOPT to include –regex, and -LC so that regular expressions will be used (note man echo
will return many man pages then) and that they will be shown in English. This feature is handy to change the default behaviour of applications (either system, user or directory-wide).
kdb set system/env/override/HTTP_PROXY http://proxy.hogege.com:8000/
Will permanently and system-wide change the proxy for all applications that honor HTTP_PROXY, e.g. w3m. We can also link http_proxy
to the value of HTTP_PROXY
:
kdb setmeta spec/env/override/http_proxy "override/#0" /env/override/HTTP_PROXY kdb get /env/override/http_proxy