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 * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
  17   chroot() environment. This is particularly relevant for systemctl, as it will
  18   not alter its behaviour for chroot() environments if set. (Normally it
  19   refrains from talking to PID 1 in such a case.)
  20
  21 * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
  22   will print latency information at runtime.
  23
  24 systemctl:
  25
  26 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
  27   listener, and instead always connect through the dbus-daemon D-bus broker.
  28
  29 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
  30   the client side, instead of asking PID 1 to do this.
  31
  32 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
  33
  34 systemd-nspawn:
  35
  36 * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
  37   hierarchy mode.
  38
  39 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
  40   friends writable in the container. If set to "network", leave only
  41   /proc/sys/net writable.
  42
  43 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
  44   uses to register with machined. If unset defaults to "nspawn", but with this
  45   variable may be set to any other value.
  46
  47 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
  48   it is available.
  49
  50 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
  51
  52 systemd-logind:
  53
  54 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
  55   hibernation is available even if the swap devices do not provide enough room
  56   for it.