125 lines
5.6 KiB
Markdown
125 lines
5.6 KiB
Markdown
# Known Environment Variables
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A number of systemd components take additional runtime parameters via
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environment variables. Many of these environment variables are not supported at
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the same level as command line switches and other interfaces are: we don't
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document them in the man pages and we make no stability guarantees for
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them. While they generally are unlikely to be dropped any time soon again, we
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do not want to guarantee that they stay around for good either.
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Below is an (incomprehensive) list of the environment variables understood by
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the various tools. Note that this list only covers environment variables not
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documented in the proper man pages.
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All tools:
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* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
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refrain from talking to PID 1; this has the same effect as the historical
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detection of `chroot()`. Setting this variable to `0` instead has a similar
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effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
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communicate with PID 1 even if a `chroot()` environment is detected.
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You almost certainly want to set this to `1` if you maintain a package build system
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or similar and are trying to use a modern container system and not plain
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`chroot()`.
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* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
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`chroot()` environment. This is particularly relevant for systemctl, as it
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will not alter its behaviour for `chroot()` environments if set. Normally it
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refrains from talking to PID 1 in such a case; turning most operations such
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as `start` into no-ops. If that's what's explicitly desired, you might
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consider setting `SYSTEMD_OFFLINE=1`.
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* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
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will print latency information at runtime.
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* `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel
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command line instead of the actual one readable from /proc/cmdline. This is
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useful for debugging, in order to test generators and other code against
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specific kernel command lines.
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* `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
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completion. If no time unit is specified, assumes seconds. The usual other units
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are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
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to 0, then the built-in default is used.
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* `$SYSTEMD_MEMPOOL=0` — if set the internal memory caching logic employed by
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hash tables is turned off, and libc malloc() is used for all allocations.
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systemctl:
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* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
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listener, and instead always connect through the dbus-daemon D-bus broker.
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* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
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the client side, instead of asking PID 1 to do this.
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* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
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systemd-nspawn:
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* `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
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hierarchy mode.
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* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
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friends writable in the container. If set to "network", leave only
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/proc/sys/net writable.
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* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
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uses to register with machined. If unset defaults to "nspawn", but with this
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variable may be set to any other value.
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* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
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it is available.
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* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
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systemd-logind:
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* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
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hibernation is available even if the swap devices do not provide enough room
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for it.
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installed systemd tests:
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* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
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a test executable is moved to an arbitrary location.
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nss-systemd:
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* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
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user/group records for the `root` and `nobody` users if they are missing from
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`/etc/passwd`.
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* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
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user/group records for dynamically registered service users (i.e. users
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registered through `DynamicUser=1`).
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* `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
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dynamic user lookups. This is primarily useful to make `nss-systemd` work
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safely from within `dbus-daemon`.
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systemd-timedated:
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* `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
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NTP client services. If set, `timedatectl set-ntp on` enables and starts the
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first existing unit listed in the environment variable, and
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`timedatectl set-ntp off` disables and stops all listed units.
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systemd itself:
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* `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
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are done by the service manager on behalf of a specific unit, in child
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processes that are later (after execve()) going to become unit
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processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
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modules can use this information to determine in which context and on whose
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behalf they are being called, which may be useful to avoid deadlocks, for
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example to bypass IPC calls to the very service that is about to be
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started. Note that NSS and PAM modules should be careful to only rely on this
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data when invoked privileged, or possibly only when getppid() returns 1, as
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setting environment variables is of course possible in any even unprivileged
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contexts.
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* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
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it is either set to `system` or `user` depending on whether the NSS/PAM
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module is called by systemd in `--system` or `--user` mode.
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