systemd.environment-generator(7) — Linux manual page



NAME         top

       systemd.environment-generator - systemd environment file generators

SYNOPSIS         top





DESCRIPTION         top

       Generators are small executables that live in
       /usr/lib/systemd/system-environment-generators/ and other directories
       listed above.  systemd(1) will execute those binaries very early at
       the startup of each manager and at configuration reload time, before
       running the generators described in systemd.generator(7) and before
       starting any units. Environment generators can override the
       environment that the manager exports to services and other processes.

       Generators are loaded from a set of paths determined during
       compilation, as listed above. System and user environment generators
       are loaded from directories with names ending in
       system-environment-generators/ and user-environment-generators/,
       respectively. Generators found in directories listed earlier override
       the ones with the same name in directories lower in the list. A
       symlink to /dev/null or an empty file can be used to mask a
       generator, thereby preventing it from running. Please note that the
       order of the two directories with the highest priority is reversed
       with respect to the unit load path, and generators in /run/ overwrite
       those in /etc/.

       After installing new generators or updating the configuration,
       systemctl daemon-reload may be executed. This will re-run all
       generators, updating environment configuration. It will be used for
       any services that are started subsequently.

       Environment file generators are executed similarly to unit file
       generators described in systemd.generator(7), with the following

       •   Generators are executed sequentially in the alphanumerical order
           of the final component of their name. The output of each
           generator output is immediately parsed and used to update the
           environment for generators that run after that. Thus, later
           generators can use and/or modify the output of earlier

       •   Generators are run by every manager instance, their output can be
           different for each user.

       It is recommended to use numerical prefixes for generator names to
       simplify ordering.

EXAMPLES         top

       Example 1. A simple generator that extends an environment variable if
       a directory exists in the file system



           # set the default value

           # add a directory if it exists
           if [[ -d /opt/foo/share ]]; then

           # write our output
           echo XDG_DATA_DIRS=$XDG_DATA_DIRS

       Example 2. A more complicated generator which reads existing
       configuration and mutates one variable


           #!/usr/bin/env python3


           Proof-of-concept systemd environment generator that makes sure that bin dirs
           are always after matching sbin dirs in the path.
           (Changes /sbin:/bin:/foo/bar to /bin:/sbin:/foo/bar.)

           This generator shows how to override the configuration possibly created by
           earlier generators. It would be easier to write in bash, but let's have it
           in Python just to prove that we can, and to serve as a template for more
           interesting generators.


           import os
           import pathlib

           def rearrange_bin_sbin(path):
               """Make sure any pair of .../bin, .../sbin directories is in this order

               >>> rearrange_bin_sbin('/bin:/sbin:/usr/sbin:/usr/bin')
               items = [pathlib.Path(p) for p in path.split(':')]
               for i in range(len(items)):
                   if 'sbin' in items[i].parts:
                       ind = items[i].parts.index('sbin')
                       bin = pathlib.Path(*items[i].parts[:ind], 'bin', *items[i].parts[ind+1:])
                       if bin in items[i+1:]:
                           j = i + 1 + items[i+1:].index(bin)
                           items[i], items[j] = items[j], items[i]
               return ':'.join(p.as_posix() for p in items)

           if __name__ == '__main__':
               path = os.environ['PATH'] # This should be always set.
                                         # If it's not, we'll just crash, we is OK too.
               new = rearrange_bin_sbin(path)
               if new != path:

       Example 3. Debugging a generator

           SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \

SEE ALSO         top

       systemd-environment-d-generator(8), systemd.generator(7), systemd(1),

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
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       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                 SYSTEMD.ENVIRONMENT-GENERATOR(7)

Pages that refer to this page: environment.d(5)systemd.unit(5)30-systemd-environment-d-generator(7)systemd.directives(7)systemd.generator(7)systemd.index(7)30-systemd-environment-d-generator(8)systemd-environment-d-generator(8)