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c3e270f4 FB |
1 | --- |
2 | title: Known Environment Variables | |
3 | --- | |
4 | ||
4549fcdb LP |
5 | # Known Environment Variables |
6 | ||
7 | A number of systemd components take additional runtime parameters via | |
8 | environment variables. Many of these environment variables are not supported at | |
9 | the same level as command line switches and other interfaces are: we don't | |
10 | document them in the man pages and we make no stability guarantees for | |
11 | them. While they generally are unlikely to be dropped any time soon again, we | |
12 | do not want to guarantee that they stay around for good either. | |
13 | ||
14 | Below is an (incomprehensive) list of the environment variables understood by | |
15 | the various tools. Note that this list only covers environment variables not | |
16 | documented in the proper man pages. | |
17 | ||
18 | All tools: | |
19 | ||
f38951a6 CW |
20 | * `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will |
21 | refrain from talking to PID 1; this has the same effect as the historical | |
22 | detection of `chroot()`. Setting this variable to `0` instead has a similar | |
23 | effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to | |
24 | communicate with PID 1 even if a `chroot()` environment is detected. | |
25 | You almost certainly want to set this to `1` if you maintain a package build system | |
26 | or similar and are trying to use a modern container system and not plain | |
27 | `chroot()`. | |
28 | ||
4549fcdb | 29 | * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a |
f38951a6 CW |
30 | `chroot()` environment. This is particularly relevant for systemctl, as it |
31 | will not alter its behaviour for `chroot()` environments if set. Normally it | |
32 | refrains from talking to PID 1 in such a case; turning most operations such | |
33 | as `start` into no-ops. If that's what's explicitly desired, you might | |
34 | consider setting `SYSTEMD_OFFLINE=1`. | |
4549fcdb LP |
35 | |
36 | * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation | |
37 | will print latency information at runtime. | |
38 | ||
2467cc55 LP |
39 | * `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel |
40 | command line instead of the actual one readable from /proc/cmdline. This is | |
41 | useful for debugging, in order to test generators and other code against | |
42 | specific kernel command lines. | |
43 | ||
0307ea49 ZJS |
44 | * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection. |
45 | This is useful for debugging and testing initrd-only programs in the main | |
46 | system. | |
47 | ||
385b2eb2 YW |
48 | * `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call |
49 | completion. If no time unit is specified, assumes seconds. The usual other units | |
50 | are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set | |
51 | to 0, then the built-in default is used. | |
52 | ||
5f1b0cc6 | 53 | * `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by |
b4f60743 LP |
54 | hash tables is turned off, and libc malloc() is used for all allocations. |
55 | ||
5f1b0cc6 LP |
56 | * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will |
57 | not output graphical smiley emojis, but ASCII alternatives instead. Note that | |
58 | this only controls use of Unicode emoji glyphs, and has no effect on other | |
59 | Unicode glyphs. | |
60 | ||
4549fcdb LP |
61 | systemctl: |
62 | ||
63 | * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus | |
64 | listener, and instead always connect through the dbus-daemon D-bus broker. | |
65 | ||
66 | * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on | |
67 | the client side, instead of asking PID 1 to do this. | |
68 | ||
69 | * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks. | |
70 | ||
71 | systemd-nspawn: | |
72 | ||
73 | * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup | |
74 | hierarchy mode. | |
75 | ||
76 | * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and | |
77 | friends writable in the container. If set to "network", leave only | |
78 | /proc/sys/net writable. | |
79 | ||
80 | * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn | |
81 | uses to register with machined. If unset defaults to "nspawn", but with this | |
82 | variable may be set to any other value. | |
83 | ||
84 | * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if | |
85 | it is available. | |
86 | ||
87 | * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running. | |
88 | ||
1099ceeb LP |
89 | * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the |
90 | container with a tmpfs, but leave the directory from the image in place. | |
91 | ||
4549fcdb LP |
92 | systemd-logind: |
93 | ||
94 | * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that | |
95 | hibernation is available even if the swap devices do not provide enough room | |
96 | for it. | |
94fa1497 | 97 | |
7db43ec3 LP |
98 | systemd-udevd: |
99 | ||
f7e81fd9 | 100 | * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of |
06da5c63 ZJS |
101 | "v238", "v239", "v240"…, or the special value "latest") as parameter. If |
102 | specified udev's net_id builtin will follow the specified naming scheme when | |
103 | determining stable network interface names. This may be used to revert to | |
104 | naming schemes of older udev versions, in order to provide more stable naming | |
105 | across updates. This environment variable takes precedence over the kernel | |
106 | command line option `net.naming-scheme=`, except if the value is prefixed | |
107 | with `:` in which case the kernel command line option takes precedence, if it | |
108 | is specified as well. | |
f7e81fd9 | 109 | |
94fa1497 ZJS |
110 | installed systemd tests: |
111 | ||
112 | * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if | |
113 | a test executable is moved to an arbitrary location. | |
dba1bd43 LP |
114 | |
115 | nss-systemd: | |
116 | ||
117 | * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize | |
118 | user/group records for the `root` and `nobody` users if they are missing from | |
119 | `/etc/passwd`. | |
120 | ||
121 | * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return | |
122 | user/group records for dynamically registered service users (i.e. users | |
123 | registered through `DynamicUser=1`). | |
124 | ||
125 | * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do | |
126 | dynamic user lookups. This is primarily useful to make `nss-systemd` work | |
127 | safely from within `dbus-daemon`. | |
41d0da0f YW |
128 | |
129 | systemd-timedated: | |
130 | ||
131 | * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of | |
132 | NTP client services. If set, `timedatectl set-ntp on` enables and starts the | |
133 | first existing unit listed in the environment variable, and | |
134 | `timedatectl set-ntp off` disables and stops all listed units. | |
39922217 | 135 | |
33eb44fe AH |
136 | systemd-sulogin-shell: |
137 | ||
138 | * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the | |
139 | root password is not available (such as when the root account is locked). | |
140 | See `sulogin(8)` for more details. | |
141 | ||
8cbb7d87 LP |
142 | bootctl and other tools that access the EFI System Partition (ESP): |
143 | ||
144 | * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are | |
145 | relaxed. Specifically, validation checks that ensure the specified ESP path | |
146 | is a FAT file system are turned off, as are checks that the path is located | |
147 | on a GPT partition with the correct type UUID. | |
148 | ||
cc7a0bfa LP |
149 | * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This |
150 | may be used to override ESP path auto detection, and redirect any accesses to | |
151 | the ESP to the specified directory. Not that unlike with bootctl's --path= | |
152 | switch only very superficial validation of the specified path is done when | |
153 | this environment variable is used. | |
154 | ||
39922217 LP |
155 | systemd itself: |
156 | ||
157 | * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that | |
158 | are done by the service manager on behalf of a specific unit, in child | |
159 | processes that are later (after execve()) going to become unit | |
160 | processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM | |
161 | modules can use this information to determine in which context and on whose | |
162 | behalf they are being called, which may be useful to avoid deadlocks, for | |
163 | example to bypass IPC calls to the very service that is about to be | |
164 | started. Note that NSS and PAM modules should be careful to only rely on this | |
165 | data when invoked privileged, or possibly only when getppid() returns 1, as | |
166 | setting environment variables is of course possible in any even unprivileged | |
167 | contexts. | |
168 | ||
169 | * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`, | |
170 | it is either set to `system` or `user` depending on whether the NSS/PAM | |
171 | module is called by systemd in `--system` or `--user` mode. | |
59f13dd6 LP |
172 | |
173 | systemd-remount-fs: | |
174 | ||
175 | * `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory | |
176 | exists in /etc/fstab (this file always takes precedence), then the root | |
177 | directory is remounted writable. This is primarily used by | |
178 | systemd-gpt-auto-generator to ensure the root partition is mounted writable | |
179 | in accordance to the GPT partition flags. |