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


SYSTEMD...ENERATOR(7) systemd.environment-generatorSYSTEMD...ENERATOR(7)

NAME         top

       systemd.environment-generator - systemd environment file

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.

       •   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


           # SPDX-License-Identifier: MIT-0

           # 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
           # SPDX-License-Identifier: MIT-0


           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, which 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), systemctl(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 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                        SYSTEMD...ENERATOR(7)

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