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 * `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
  50   hash tables is turned off, and libc malloc() is used for all allocations.
  51
  52 * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
  53   not output graphical smiley emojis, but ASCII alternatives instead. Note that
  54   this only controls use of Unicode emoji glyphs, and has no effect on other
  55   Unicode glyphs.
  56
  57 systemctl:
  58
  59 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
  60   listener, and instead always connect through the dbus-daemon D-bus broker.
  61
  62 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
  63   the client side, instead of asking PID 1 to do this.
  64
  65 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
  66
  67 systemd-nspawn:
  68
  69 * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
  70   hierarchy mode.
  71
  72 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
  73   friends writable in the container. If set to "network", leave only
  74   /proc/sys/net writable.
  75
  76 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
  77   uses to register with machined. If unset defaults to "nspawn", but with this
  78   variable may be set to any other value.
  79
  80 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
  81   it is available.
  82
  83 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
  84
  85 * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
  86   container with a tmpfs, but leave the directory from the image in place.
  87
  88 systemd-logind:
  89
  90 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
  91   hibernation is available even if the swap devices do not provide enough room
  92   for it.
  93
  94 systemd-udevd:
  95
  96 * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
  97   "v238", "v239", "v240"…, or the special value "latest") as parameter. If
  98   specified udev's net_id builtin will follow the specified naming scheme when
  99   determining stable network interface names. This may be used to revert to
 100   naming schemes of older udev versions, in order to provide more stable naming
 101   across updates. This environment variable takes precedence over the kernel
 102   command line option `net.naming-scheme=`, except if the value is prefixed
 103   with `:` in which case the kernel command line option takes precedence, if it
 104   is specified as well.
 105
 106 installed systemd tests:
 107
 108 * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
 109   a test executable is moved to an arbitrary location.
 110
 111 nss-systemd:
 112
 113 * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
 114   user/group records for the `root` and `nobody` users if they are missing from
 115   `/etc/passwd`.
 116
 117 * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
 118   user/group records for dynamically registered service users (i.e. users
 119   registered through `DynamicUser=1`).
 120
 121 * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
 122   dynamic user lookups. This is primarily useful to make `nss-systemd` work
 123   safely from within `dbus-daemon`.
 124
 125 systemd-timedated:
 126
 127 * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
 128   NTP client services. If set, `timedatectl set-ntp on` enables and starts the
 129   first existing unit listed in the environment variable, and
 130   `timedatectl set-ntp off` disables and stops all listed units.
 131
 132 systemd-sulogin-shell:
 133
 134 * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
 135   root password is not available (such as when the root account is locked).
 136   See `sulogin(8)` for more details.
 137
 138 bootctl and other tools that access the EFI System Partition (ESP):
 139
 140 * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
 141   relaxed. Specifically, validation checks that ensure the specified ESP path
 142   is a FAT file system are turned off, as are checks that the path is located
 143   on a GPT partition with the correct type UUID.
 144
 145 * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
 146   may be used to override ESP path auto detection, and redirect any accesses to
 147   the ESP to the specified directory. Not that unlike with bootctl's --path=
 148   switch only very superficial validation of the specified path is done when
 149   this environment variable is used.
 150
 151 systemd itself:
 152
 153 * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
 154   are done by the service manager on behalf of a specific unit, in child
 155   processes that are later (after execve()) going to become unit
 156   processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
 157   modules can use this information to determine in which context and on whose
 158   behalf they are being called, which may be useful to avoid deadlocks, for
 159   example to bypass IPC calls to the very service that is about to be
 160   started. Note that NSS and PAM modules should be careful to only rely on this
 161   data when invoked privileged, or possibly only when getppid() returns 1, as
 162   setting environment variables is of course possible in any even unprivileged
 163   contexts.
 164
 165 * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
 166   it is either set to `system` or `user` depending on whether the NSS/PAM
 167   module is called by systemd in `--system` or `--user` mode.