systemd.environment-generator(7)

1SYSTEMD.ENVIRONMENT-GENERAsTyOsRt(e7m)d.environment-geSnYeSrTaEtMoDr.ENVIRONMENT-GENERATOR(7)
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NAME

6       systemd.environment-generator - systemd environment file generators
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SYNOPSIS

9       /usr/lib/systemd/system-environment-generators/some-generator
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11       /usr/lib/systemd/user-environment-generators/some-generator
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13       /run/systemd/system-environment-generators/*
14       /etc/systemd/system-environment-generators/*
15       /usr/local/lib/systemd/system-environment-generators/*
16       /usr/lib/systemd/system-environment-generators/*
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18       /run/systemd/user-environment-generators/*
19       /etc/systemd/user-environment-generators/*
20       /usr/local/lib/systemd/user-environment-generators/*
21       /usr/lib/systemd/user-environment-generators/*
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DESCRIPTION

25       Generators are small executables that live in
26       /usr/lib/systemd/system-environment-generators/ and other directories
27       listed above.  systemd(1) will execute those binaries very early at the
28       startup of each manager and at configuration reload time, before
29       running the generators described in systemd.generator(7) and before
30       starting any units. Environment generators can override the environment
31       that the manager exports to services and other processes.
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33       Generators are loaded from a set of paths determined during
34       compilation, as listed above. System and user environment generators
35       are loaded from directories with names ending in
36       system-environment-generators/ and user-environment-generators/,
37       respectively. Generators found in directories listed earlier override
38       the ones with the same name in directories lower in the list. A symlink
39       to /dev/null or an empty file can be used to mask a generator, thereby
40       preventing it from running. Please note that the order of the two
41       directories with the highest priority is reversed with respect to the
42       unit load path, and generators in /run/ overwrite those in /etc/.
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44       After installing new generators or updating the configuration,
45       systemctl daemon-reload may be executed. This will re-run all
46       generators, updating environment configuration. It will be used for any
47       services that are started subsequently.
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49       Environment file generators are executed similarly to unit file
50       generators described in systemd.generator(7), with the following
51       differences:
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53       •   Generators are executed sequentially in the alphanumerical order of
54           the final component of their name. The output of each generator
55           output is immediately parsed and used to update the environment for
56           generators that run after that. Thus, later generators can use
57           and/or modify the output of earlier generators.
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59       •   Generators are run by every manager instance, their output can be
60           different for each user.
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62       It is recommended to use numerical prefixes for generator names to
63       simplify ordering.
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EXAMPLES

66       Example 1. A simple generator that extends an environment variable if a
67       directory exists in the file system
68
69           # 50-xdg-data-dirs.sh
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71           #!/bin/sh
72           # SPDX-License-Identifier: MIT-0
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74           # set the default value
75           XDG_DATA_DIRS="${XDG_DATA_DIRS:-/usr/local/share/:/usr/share}"
76
77           # add a directory if it exists
78           if [ -d /opt/foo/share ]; then
79               XDG_DATA_DIRS="/opt/foo/share:${XDG_DATA_DIRS}"
80           fi
81
82           # write our output
83           echo "XDG_DATA_DIRS=${XDG_DATA_DIRS}"
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85       Example 2. A more complicated generator which reads existing
86       configuration and mutates one variable
87
88           # 90-rearrange-path.py
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90           #!/usr/bin/env python3
91           # SPDX-License-Identifier: MIT-0
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93           """
94
95           Proof-of-concept systemd environment generator that makes sure that bin dirs
96           are always after matching sbin dirs in the path.
97           (Changes /sbin:/bin:/foo/bar to /bin:/sbin:/foo/bar.)
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99           This generator shows how to override the configuration possibly created by
100           earlier generators. It would be easier to write in bash, but let's have it
101           in Python just to prove that we can, and to serve as a template for more
102           interesting generators.
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104           """
105
106           import os
107           import pathlib
108
109           def rearrange_bin_sbin(path):
110               """Make sure any pair of .../bin, .../sbin directories is in this order
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112               >>> rearrange_bin_sbin('/bin:/sbin:/usr/sbin:/usr/bin')
113               '/bin:/sbin:/usr/bin:/usr/sbin'
114               """
115               items = [pathlib.Path(p) for p in path.split(':')]
116               for i in range(len(items)):
117                   if 'sbin' in items[i].parts:
118                       ind = items[i].parts.index('sbin')
119                       bin = pathlib.Path(*items[i].parts[:ind], 'bin', *items[i].parts[ind+1:])
120                       if bin in items[i+1:]:
121                           j = i + 1 + items[i+1:].index(bin)
122                           items[i], items[j] = items[j], items[i]
123               return ':'.join(p.as_posix() for p in items)
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125           if __name__ == '__main__':
126               path = os.environ['PATH'] # This should be always set.
127                                         # If it's not, we'll just crash, which is OK too.
128               new = rearrange_bin_sbin(path)
129               if new != path:
130                   print('PATH={}'.format(new))
131
132       Example 3. Debugging a generator
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134           SYSTEMD_LOG_LEVEL=debug VAR_A=something VAR_B="something else" \
135           /usr/lib/systemd/system-environment-generators/path-to-generator
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NAME

SYNOPSIS

DESCRIPTION

EXAMPLES

SEE ALSO