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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 | ||
0307ea49 ZJS |
40 | * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection. |
41 | This is useful for debugging and testing initrd-only programs in the main | |
42 | system. | |
43 | ||
385b2eb2 YW |
44 | * `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call |
45 | completion. If no time unit is specified, assumes seconds. The usual other units | |
46 | are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set | |
47 | to 0, then the built-in default is used. | |
48 | ||
5f1b0cc6 | 49 | * `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by |
b4f60743 LP |
50 | hash tables is turned off, and libc malloc() is used for all allocations. |
51 | ||
5f1b0cc6 LP |
52 | * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will |
53 | not output graphical smiley emojis, but ASCII alternatives instead. Note that | |
54 | this only controls use of Unicode emoji glyphs, and has no effect on other | |
55 | Unicode glyphs. | |
56 | ||
4549fcdb LP |
57 | systemctl: |
58 | ||
59 | * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus | |
60 | listener, and instead always connect through the dbus-daemon D-bus broker. | |
61 | ||
62 | * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on | |
63 | the client side, instead of asking PID 1 to do this. | |
64 | ||
65 | * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks. | |
66 | ||
67 | systemd-nspawn: | |
68 | ||
69 | * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup | |
70 | hierarchy mode. | |
71 | ||
72 | * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and | |
73 | friends writable in the container. If set to "network", leave only | |
74 | /proc/sys/net writable. | |
75 | ||
76 | * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn | |
77 | uses to register with machined. If unset defaults to "nspawn", but with this | |
78 | variable may be set to any other value. | |
79 | ||
80 | * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if | |
81 | it is available. | |
82 | ||
83 | * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running. | |
84 | ||
1099ceeb LP |
85 | * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the |
86 | container with a tmpfs, but leave the directory from the image in place. | |
87 | ||
4549fcdb LP |
88 | systemd-logind: |
89 | ||
90 | * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that | |
91 | hibernation is available even if the swap devices do not provide enough room | |
92 | for it. | |
94fa1497 | 93 | |
f7e81fd9 | 94 | * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of |
06da5c63 ZJS |
95 | "v238", "v239", "v240"…, or the special value "latest") as parameter. If |
96 | specified udev's net_id builtin will follow the specified naming scheme when | |
97 | determining stable network interface names. This may be used to revert to | |
98 | naming schemes of older udev versions, in order to provide more stable naming | |
99 | across updates. This environment variable takes precedence over the kernel | |
100 | command line option `net.naming-scheme=`, except if the value is prefixed | |
101 | with `:` in which case the kernel command line option takes precedence, if it | |
102 | is specified as well. | |
f7e81fd9 | 103 | |
94fa1497 ZJS |
104 | installed systemd tests: |
105 | ||
106 | * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if | |
107 | a test executable is moved to an arbitrary location. | |
dba1bd43 LP |
108 | |
109 | nss-systemd: | |
110 | ||
111 | * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize | |
112 | user/group records for the `root` and `nobody` users if they are missing from | |
113 | `/etc/passwd`. | |
114 | ||
115 | * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return | |
116 | user/group records for dynamically registered service users (i.e. users | |
117 | registered through `DynamicUser=1`). | |
118 | ||
119 | * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do | |
120 | dynamic user lookups. This is primarily useful to make `nss-systemd` work | |
121 | safely from within `dbus-daemon`. | |
41d0da0f YW |
122 | |
123 | systemd-timedated: | |
124 | ||
125 | * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of | |
126 | NTP client services. If set, `timedatectl set-ntp on` enables and starts the | |
127 | first existing unit listed in the environment variable, and | |
128 | `timedatectl set-ntp off` disables and stops all listed units. | |
39922217 | 129 | |
33eb44fe AH |
130 | systemd-sulogin-shell: |
131 | ||
132 | * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the | |
133 | root password is not available (such as when the root account is locked). | |
134 | See `sulogin(8)` for more details. | |
135 | ||
8cbb7d87 LP |
136 | bootctl and other tools that access the EFI System Partition (ESP): |
137 | ||
138 | * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are | |
139 | relaxed. Specifically, validation checks that ensure the specified ESP path | |
140 | is a FAT file system are turned off, as are checks that the path is located | |
141 | on a GPT partition with the correct type UUID. | |
142 | ||
cc7a0bfa LP |
143 | * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This |
144 | may be used to override ESP path auto detection, and redirect any accesses to | |
145 | the ESP to the specified directory. Not that unlike with bootctl's --path= | |
146 | switch only very superficial validation of the specified path is done when | |
147 | this environment variable is used. | |
148 | ||
39922217 LP |
149 | systemd itself: |
150 | ||
151 | * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that | |
152 | are done by the service manager on behalf of a specific unit, in child | |
153 | processes that are later (after execve()) going to become unit | |
154 | processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM | |
155 | modules can use this information to determine in which context and on whose | |
156 | behalf they are being called, which may be useful to avoid deadlocks, for | |
157 | example to bypass IPC calls to the very service that is about to be | |
158 | started. Note that NSS and PAM modules should be careful to only rely on this | |
159 | data when invoked privileged, or possibly only when getppid() returns 1, as | |
160 | setting environment variables is of course possible in any even unprivileged | |
161 | contexts. | |
162 | ||
163 | * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`, | |
164 | it is either set to `system` or `user` depending on whether the NSS/PAM | |
165 | module is called by systemd in `--system` or `--user` mode. |