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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 | * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of |
06da5c63 ZJS |
101 | "v238", "v239", "v240"…, or the special value "latest") as parameter. If |
102 | specified udev's net_id builtin will follow the specified naming scheme when | |
103 | determining stable network interface names. This may be used to revert to | |
104 | naming schemes of older udev versions, in order to provide more stable naming | |
105 | across updates. This environment variable takes precedence over the kernel | |
106 | command line option `net.naming-scheme=`, except if the value is prefixed | |
107 | with `:` in which case the kernel command line option takes precedence, if it | |
108 | is specified as well. | |
f7e81fd9 | 109 | |
e86c7a3a LP |
110 | * `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set overrides systemd-logind's |
111 | built-in EFI logic of requesting a reboot into the firmware. Takes a | |
112 | boolean. If set to false the functionality is turned off entirely. If set to | |
113 | true instead of requesting a reboot into the firmware setup UI through EFI a | |
114 | file `/run/systemd/reboot-to-firmware-setup` is created whenever this is | |
115 | requested. This file may be checked for by services run during system | |
116 | shutdown in order to request the appropriate operation from the firmware in | |
117 | an alternative fashion. | |
118 | ||
119 | * `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows | |
120 | overriding of systemd-logind's built-in EFI logic of requesting a reboot into | |
121 | the boot loader menu. Takes a boolean. If set to false the functionality is | |
122 | turned off entirely. If set to true instead of requesting a reboot into the | |
123 | boot loader menu through EFI a file `/run/systemd/reboot-to-boot-loader-menu` | |
124 | is created whenever this is requested. The file contains the requested boot | |
125 | loader menu timeout in µs, formatted in ASCII decimals, or zero in case no | |
126 | time-out is requested. This file may be checked for by services run during | |
127 | system shutdown in order to request the appropriate operation from the boot | |
128 | loader in an alternative fashion. | |
129 | ||
130 | * `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows | |
131 | overriding of systemd-logind's built-in EFI logic of requesting a reboot into | |
132 | a specific boot loader entry. Takes a boolean. If set to false the | |
133 | functionality is turned off entirely. If set to true instead of requesting a | |
134 | reboot into a specific boot loader entry through EFI a file | |
135 | `/run/systemd/reboot-to-boot-loader-entry` is created whenever this is | |
136 | requested. The file contains the requested boot loader entry identifier. This | |
137 | file may be checked for by services run during system shutdown in order to | |
138 | request the appropriate operation from the boot loader in an alternative | |
139 | fashion. Note that by default only boot loader entries which follow the [Boot | |
140 | Loader Specification](https://systemd.io/BOOT_LOADER_SPECIFICATION) and are | |
141 | placed in the ESP or the Extended Boot Loader partition may be selected this | |
142 | way. However, if a directory `/run/boot-loader-entries/` exists, the entries | |
143 | are loaded from there instead. The directory should contain the usual | |
144 | directory hierarchy mandated by the Boot Loader Specification, i.e. the entry | |
145 | drop-ins should be placed in | |
146 | `/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by | |
147 | the drop-ins (including the kernels and initrds) somewhere else below | |
148 | `/run/boot-loader-entries/`. Note that all these files may be (and are | |
149 | supposed to be) symlinks. systemd-logind will load these files on-demand, | |
150 | these files can hence be updated (ideally atomically) whenever the boot | |
151 | loader configuration changes. A foreign boot loader installer script should | |
152 | hence synthesize drop-in snippets and symlinks for all boot entries at boot | |
153 | or whenever they change if it wants to integrate with systemd-logind's APIs. | |
154 | ||
94fa1497 ZJS |
155 | installed systemd tests: |
156 | ||
157 | * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if | |
158 | a test executable is moved to an arbitrary location. | |
dba1bd43 LP |
159 | |
160 | nss-systemd: | |
161 | ||
162 | * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize | |
163 | user/group records for the `root` and `nobody` users if they are missing from | |
164 | `/etc/passwd`. | |
165 | ||
166 | * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return | |
167 | user/group records for dynamically registered service users (i.e. users | |
168 | registered through `DynamicUser=1`). | |
169 | ||
170 | * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do | |
171 | dynamic user lookups. This is primarily useful to make `nss-systemd` work | |
172 | safely from within `dbus-daemon`. | |
41d0da0f YW |
173 | |
174 | systemd-timedated: | |
175 | ||
176 | * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of | |
177 | NTP client services. If set, `timedatectl set-ntp on` enables and starts the | |
178 | first existing unit listed in the environment variable, and | |
179 | `timedatectl set-ntp off` disables and stops all listed units. | |
39922217 | 180 | |
33eb44fe AH |
181 | systemd-sulogin-shell: |
182 | ||
183 | * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the | |
184 | root password is not available (such as when the root account is locked). | |
185 | See `sulogin(8)` for more details. | |
186 | ||
8cbb7d87 LP |
187 | bootctl and other tools that access the EFI System Partition (ESP): |
188 | ||
189 | * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are | |
190 | relaxed. Specifically, validation checks that ensure the specified ESP path | |
191 | is a FAT file system are turned off, as are checks that the path is located | |
192 | on a GPT partition with the correct type UUID. | |
193 | ||
cc7a0bfa LP |
194 | * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This |
195 | may be used to override ESP path auto detection, and redirect any accesses to | |
196 | the ESP to the specified directory. Not that unlike with bootctl's --path= | |
197 | switch only very superficial validation of the specified path is done when | |
198 | this environment variable is used. | |
199 | ||
39922217 LP |
200 | systemd itself: |
201 | ||
202 | * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that | |
203 | are done by the service manager on behalf of a specific unit, in child | |
204 | processes that are later (after execve()) going to become unit | |
205 | processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM | |
206 | modules can use this information to determine in which context and on whose | |
207 | behalf they are being called, which may be useful to avoid deadlocks, for | |
208 | example to bypass IPC calls to the very service that is about to be | |
209 | started. Note that NSS and PAM modules should be careful to only rely on this | |
210 | data when invoked privileged, or possibly only when getppid() returns 1, as | |
211 | setting environment variables is of course possible in any even unprivileged | |
212 | contexts. | |
213 | ||
214 | * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`, | |
215 | it is either set to `system` or `user` depending on whether the NSS/PAM | |
216 | module is called by systemd in `--system` or `--user` mode. | |
59f13dd6 LP |
217 | |
218 | systemd-remount-fs: | |
219 | ||
d238709c | 220 | * `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and no entry for the root directory |
59f13dd6 LP |
221 | exists in /etc/fstab (this file always takes precedence), then the root |
222 | directory is remounted writable. This is primarily used by | |
223 | systemd-gpt-auto-generator to ensure the root partition is mounted writable | |
224 | in accordance to the GPT partition flags. | |
a7d9fccd LP |
225 | |
226 | systemd-firstboot and localectl: | |
227 | ||
228 | * `SYSTEMD_LIST_NON_UTF8_LOCALES=1` – if set non-UTF-8 locales are listed among | |
229 | the installed ones. By default non-UTF-8 locales are suppressed from the | |
230 | selection, since we are living in the 21st century. |