ENVIRONMENT.md

   1 # Known Environment Variables
   2
   3 A number of systemd components take additional runtime parameters via
   4 environment variables. Many of these environment variables are not supported at
   5 the same level as command line switches and other interfaces are: we don't
   6 document them in the man pages and we make no stability guarantees for
   7 them. While they generally are unlikely to be dropped any time soon again, we
   8 do not want to guarantee that they stay around for good either.
   9
  10 Below is an (incomprehensive) list of the environment variables understood by
  11 the various tools. Note that this list only covers environment variables not
  12 documented in the proper man pages.
  13
  14 All tools:
  15
  16 * `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
  17   refrain from talking to PID 1; this has the same effect as the historical
  18   detection of `chroot()`.  Setting this variable to `0` instead has a similar
  19   effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
  20   communicate with PID 1 even if a `chroot()` environment is detected.
  21   You almost certainly want to set this to `1` if you maintain a package build system
  22   or similar and are trying to use a modern container system and not plain
  23   `chroot()`.
  24
  25 * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
  26   `chroot()` environment. This is particularly relevant for systemctl, as it
  27   will not alter its behaviour for `chroot()` environments if set.  Normally it
  28   refrains from talking to PID 1 in such a case; turning most operations such
  29   as `start` into no-ops.  If that's what's explicitly desired, you might
  30   consider setting `SYSTEMD_OFFLINE=1`.
  31
  32 * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
  33   will print latency information at runtime.
  34
  35 * `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel
  36   command line instead of the actual one readable from /proc/cmdline. This is
  37   useful for debugging, in order to test generators and other code against
  38   specific kernel command lines.
  39
  40 systemctl:
  41
  42 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
  43   listener, and instead always connect through the dbus-daemon D-bus broker.
  44
  45 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
  46   the client side, instead of asking PID 1 to do this.
  47
  48 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
  49
  50 systemd-nspawn:
  51
  52 * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
  53   hierarchy mode.
  54
  55 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
  56   friends writable in the container. If set to "network", leave only
  57   /proc/sys/net writable.
  58
  59 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
  60   uses to register with machined. If unset defaults to "nspawn", but with this
  61   variable may be set to any other value.
  62
  63 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
  64   it is available.
  65
  66 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
  67
  68 systemd-logind:
  69
  70 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
  71   hibernation is available even if the swap devices do not provide enough room
  72   for it.
  73
  74 installed systemd tests:
  75
  76 * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
  77   a test executable is moved to an arbitrary location.
  78
  79 nss-systemd:
  80
  81 * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
  82   user/group records for the `root` and `nobody` users if they are missing from
  83   `/etc/passwd`.
  84
  85 * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
  86   user/group records for dynamically registered service users (i.e. users
  87   registered through `DynamicUser=1`).
  88
  89 * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
  90   dynamic user lookups. This is primarily useful to make `nss-systemd` work
  91   safely from within `dbus-daemon`.