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I figure sooneror later we'll have more of these docs, hence let's give them a clean place to be. This leaves NEWS and README/README.md as well as the LICENSE texts in the root directory of the project since that appears to be customary for Free Software projects.
92 lines
3.9 KiB
Markdown
92 lines
3.9 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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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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