|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
|
|
|
SYSTEMD...ENERATOR(7) systemd.environment-generatorSYSTEMD...ENERATOR(7)
systemd.environment-generator - systemd environment file
generators
/usr/lib/systemd/system-environment-generators/some-generator
/usr/lib/systemd/user-environment-generators/some-generator
/run/systemd/system-environment-generators/*
/etc/systemd/system-environment-generators/*
/usr/local/lib/systemd/system-environment-generators/*
/usr/lib/systemd/system-environment-generators/*
/run/systemd/user-environment-generators/*
/etc/systemd/user-environment-generators/*
/usr/local/lib/systemd/user-environment-generators/*
/usr/lib/systemd/user-environment-generators/*
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 [1]. 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
differences:
• 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.
Example 1. A simple generator that extends an environment
variable if a directory exists in the file system
# 50-xdg-data-dirs.sh
#!/bin/sh
# SPDX-License-Identifier: MIT-0
# set the default value
XDG_DATA_DIRS="${XDG_DATA_DIRS:-/usr/local/share/:/usr/share}"
# add a directory if it exists
if [ -d /opt/foo/share ]; then
XDG_DATA_DIRS="/opt/foo/share:${XDG_DATA_DIRS}"
fi
# write our output
echo "XDG_DATA_DIRS=${XDG_DATA_DIRS}"
Example 2. A more complicated generator which reads existing
configuration and mutates one variable
# 90-rearrange-path.py
#!/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')
'/bin:/sbin:/usr/bin:/usr/sbin'
"""
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:
print('PATH={}'.format(new))
Example 3. Debugging a generator
SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \
/usr/lib/systemd/system-environment-generators/path-to-generator
systemd-environment-d-generator(8), systemd.generator(7),
systemd(1), systemctl(1)
1. 💣💥🧨💥💥💣 Please note that those configuration files must
be available at all times. If /usr/local/ is a separate
partition, it may not be available during early boot, and
must not be used for configuration.
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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
[email protected]
systemd 257~devel 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)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|