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diff --git a/doc/ENVIRONMENT.md b/doc/ENVIRONMENT.md new file mode 100644 index 0000000000..581bf3c238 --- /dev/null +++ b/doc/ENVIRONMENT.md @@ -0,0 +1,91 @@ +# Known Environment Variables + +A number of systemd components take additional runtime parameters via +environment variables. Many of these environment variables are not supported at +the same level as command line switches and other interfaces are: we don't +document them in the man pages and we make no stability guarantees for +them. While they generally are unlikely to be dropped any time soon again, we +do not want to guarantee that they stay around for good either. + +Below is an (incomprehensive) list of the environment variables understood by +the various tools. Note that this list only covers environment variables not +documented in the proper man pages. + +All tools: + +* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will + refrain from talking to PID 1; this has the same effect as the historical + detection of `chroot()`. Setting this variable to `0` instead has a similar + effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to + communicate with PID 1 even if a `chroot()` environment is detected. + You almost certainly want to set this to `1` if you maintain a package build system + or similar and are trying to use a modern container system and not plain + `chroot()`. + +* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a + `chroot()` environment. This is particularly relevant for systemctl, as it + will not alter its behaviour for `chroot()` environments if set. Normally it + refrains from talking to PID 1 in such a case; turning most operations such + as `start` into no-ops. If that's what's explicitly desired, you might + consider setting `SYSTEMD_OFFLINE=1`. + +* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation + will print latency information at runtime. + +* `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel + command line instead of the actual one readable from /proc/cmdline. This is + useful for debugging, in order to test generators and other code against + specific kernel command lines. + +systemctl: + +* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus + listener, and instead always connect through the dbus-daemon D-bus broker. + +* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on + the client side, instead of asking PID 1 to do this. + +* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks. + +systemd-nspawn: + +* `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup + hierarchy mode. + +* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and + friends writable in the container. If set to "network", leave only + /proc/sys/net writable. + +* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn + uses to register with machined. If unset defaults to "nspawn", but with this + variable may be set to any other value. + +* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if + it is available. + +* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running. + +systemd-logind: + +* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that + hibernation is available even if the swap devices do not provide enough room + for it. + +installed systemd tests: + +* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if + a test executable is moved to an arbitrary location. + +nss-systemd: + +* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize + user/group records for the `root` and `nobody` users if they are missing from + `/etc/passwd`. + +* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return + user/group records for dynamically registered service users (i.e. users + registered through `DynamicUser=1`). + +* `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do + dynamic user lookups. This is primarily useful to make `nss-systemd` work + safely from within `dbus-daemon`. |