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4549fcdb LP |
1 | # Known Environment Variables |
2 | ||
3 | A number of systemd components take additional runtime parameters via | |
4 | environment variables. Many of these environment variables are not supported at | |
5 | the same level as command line switches and other interfaces are: we don't | |
6 | document them in the man pages and we make no stability guarantees for | |
7 | them. While they generally are unlikely to be dropped any time soon again, we | |
8 | do not want to guarantee that they stay around for good either. | |
9 | ||
10 | Below is an (incomprehensive) list of the environment variables understood by | |
11 | the various tools. Note that this list only covers environment variables not | |
12 | documented in the proper man pages. | |
13 | ||
14 | All tools: | |
15 | ||
f38951a6 CW |
16 | * `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will |
17 | refrain from talking to PID 1; this has the same effect as the historical | |
18 | detection of `chroot()`. Setting this variable to `0` instead has a similar | |
19 | effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to | |
20 | communicate with PID 1 even if a `chroot()` environment is detected. | |
21 | You almost certainly want to set this to `1` if you maintain a package build system | |
22 | or similar and are trying to use a modern container system and not plain | |
23 | `chroot()`. | |
24 | ||
4549fcdb | 25 | * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a |
f38951a6 CW |
26 | `chroot()` environment. This is particularly relevant for systemctl, as it |
27 | will not alter its behaviour for `chroot()` environments if set. Normally it | |
28 | refrains from talking to PID 1 in such a case; turning most operations such | |
29 | as `start` into no-ops. If that's what's explicitly desired, you might | |
30 | consider setting `SYSTEMD_OFFLINE=1`. | |
4549fcdb LP |
31 | |
32 | * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation | |
33 | will print latency information at runtime. | |
34 | ||
2467cc55 LP |
35 | * `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel |
36 | command line instead of the actual one readable from /proc/cmdline. This is | |
37 | useful for debugging, in order to test generators and other code against | |
38 | specific kernel command lines. | |
39 | ||
4549fcdb LP |
40 | systemctl: |
41 | ||
42 | * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus | |
43 | listener, and instead always connect through the dbus-daemon D-bus broker. | |
44 | ||
45 | * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on | |
46 | the client side, instead of asking PID 1 to do this. | |
47 | ||
48 | * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks. | |
49 | ||
50 | systemd-nspawn: | |
51 | ||
52 | * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup | |
53 | hierarchy mode. | |
54 | ||
55 | * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and | |
56 | friends writable in the container. If set to "network", leave only | |
57 | /proc/sys/net writable. | |
58 | ||
59 | * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn | |
60 | uses to register with machined. If unset defaults to "nspawn", but with this | |
61 | variable may be set to any other value. | |
62 | ||
63 | * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if | |
64 | it is available. | |
65 | ||
66 | * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running. | |
67 | ||
68 | systemd-logind: | |
69 | ||
70 | * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that | |
71 | hibernation is available even if the swap devices do not provide enough room | |
72 | for it. | |
94fa1497 ZJS |
73 | |
74 | installed systemd tests: | |
75 | ||
76 | * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if | |
77 | a test executable is moved to an arbitrary location. | |
dba1bd43 LP |
78 | |
79 | nss-systemd: | |
80 | ||
81 | * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize | |
82 | user/group records for the `root` and `nobody` users if they are missing from | |
83 | `/etc/passwd`. | |
84 | ||
85 | * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return | |
86 | user/group records for dynamically registered service users (i.e. users | |
87 | registered through `DynamicUser=1`). | |
88 | ||
89 | * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do | |
90 | dynamic user lookups. This is primarily useful to make `nss-systemd` work | |
91 | safely from within `dbus-daemon`. | |
41d0da0f YW |
92 | |
93 | systemd-timedated: | |
94 | ||
95 | * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of | |
96 | NTP client services. If set, `timedatectl set-ntp on` enables and starts the | |
97 | first existing unit listed in the environment variable, and | |
98 | `timedatectl set-ntp off` disables and stops all listed units. |