docs/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 * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
  41   This is useful for debugging and testing initrd-only programs in the main
  42   system.
  43
  44 * `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
  45   completion. If no time unit is specified, assumes seconds. The usual other units
  46   are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
  47   to 0, then the built-in default is used.
  48
  49 * `$SYSTEMD_MEMPOOL=0` — if set the internal memory caching logic employed by
  50   hash tables is turned off, and libc malloc() is used for all allocations.
  51
  52 systemctl:
  53
  54 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
  55   listener, and instead always connect through the dbus-daemon D-bus broker.
  56
  57 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
  58   the client side, instead of asking PID 1 to do this.
  59
  60 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
  61
  62 systemd-nspawn:
  63
  64 * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
  65   hierarchy mode.
  66
  67 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
  68   friends writable in the container. If set to "network", leave only
  69   /proc/sys/net writable.
  70
  71 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
  72   uses to register with machined. If unset defaults to "nspawn", but with this
  73   variable may be set to any other value.
  74
  75 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
  76   it is available.
  77
  78 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
  79
  80 * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
  81   container with a tmpfs, but leave the directory from the image in place.
  82
  83 systemd-logind:
  84
  85 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
  86   hibernation is available even if the swap devices do not provide enough room
  87   for it.
  88
  89 installed systemd tests:
  90
  91 * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
  92   a test executable is moved to an arbitrary location.
  93
  94 nss-systemd:
  95
  96 * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
  97   user/group records for the `root` and `nobody` users if they are missing from
  98   `/etc/passwd`.
  99
 100 * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
 101   user/group records for dynamically registered service users (i.e. users
 102   registered through `DynamicUser=1`).
 103
 104 * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
 105   dynamic user lookups. This is primarily useful to make `nss-systemd` work
 106   safely from within `dbus-daemon`.
 107
 108 systemd-timedated:
 109
 110 * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
 111   NTP client services. If set, `timedatectl set-ntp on` enables and starts the
 112   first existing unit listed in the environment variable, and
 113   `timedatectl set-ntp off` disables and stops all listed units.
 114
 115 bootctl and other tools that access the EFI System Partition (ESP):
 116
 117 * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
 118   relaxed. Specifically, validation checks that ensure the specified ESP path
 119   is a FAT file system are turned off, as are checks that the path is located
 120   on a GPT partition with the correct type UUID.
 121
 122 systemd itself:
 123
 124 * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
 125   are done by the service manager on behalf of a specific unit, in child
 126   processes that are later (after execve()) going to become unit
 127   processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
 128   modules can use this information to determine in which context and on whose
 129   behalf they are being called, which may be useful to avoid deadlocks, for
 130   example to bypass IPC calls to the very service that is about to be
 131   started. Note that NSS and PAM modules should be careful to only rely on this
 132   data when invoked privileged, or possibly only when getppid() returns 1, as
 133   setting environment variables is of course possible in any even unprivileged
 134   contexts.
 135
 136 * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
 137   it is either set to `system` or `user` depending on whether the NSS/PAM
 138   module is called by systemd in `--system` or `--user` mode.