docs/ENVIRONMENT.md - systemd-stable - Rivoreo Source Code Repositories

 ---
 title: Known Environment Variables
 ---

 # Known Environment Variables

 A number of systemd components take additional runtime parameters via
 environment variables. Many of these environment variables are not supported at
 the same level as command line switches and other interfaces are: we don't
 document them in the man pages and we make no stability guarantees for
 them. While they generally are unlikely to be dropped any time soon again, we
 do not want to guarantee that they stay around for good either.

 Below is an (incomprehensive) list of the environment variables understood by
 the various tools. Note that this list only covers environment variables not
 documented in the proper man pages.

 All tools:

 * `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
   refrain from talking to PID 1; this has the same effect as the historical
   detection of `chroot()`.  Setting this variable to `0` instead has a similar
   effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
   communicate with PID 1 even if a `chroot()` environment is detected.
   You almost certainly want to set this to `1` if you maintain a package build system
   or similar and are trying to use a modern container system and not plain
   `chroot()`.

 * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
   `chroot()` environment. This is particularly relevant for systemctl, as it
   will not alter its behaviour for `chroot()` environments if set.  Normally it
   refrains from talking to PID 1 in such a case; turning most operations such
   as `start` into no-ops.  If that's what's explicitly desired, you might
   consider setting `SYSTEMD_OFFLINE=1`.

 * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
   will print latency information at runtime.

 * `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel
   command line instead of the actual one readable from /proc/cmdline. This is
   useful for debugging, in order to test generators and other code against
   specific kernel command lines.

 * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
   This is useful for debugging and testing initrd-only programs in the main
   system.

 * `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
   completion. If no time unit is specified, assumes seconds. The usual other units
   are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
   to 0, then the built-in default is used.

 * `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
   hash tables is turned off, and libc malloc() is used for all allocations.

 * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
   not output graphical smiley emojis, but ASCII alternatives instead. Note that
   this only controls use of Unicode emoji glyphs, and has no effect on other
   Unicode glyphs.

 systemctl:

 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
   listener, and instead always connect through the dbus-daemon D-bus broker.

 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
   the client side, instead of asking PID 1 to do this.

 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.

 systemd-nspawn:

 * `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
   hierarchy mode.

 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
   friends writable in the container. If set to "network", leave only
   /proc/sys/net writable.

 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
   uses to register with machined. If unset defaults to "nspawn", but with this
   variable may be set to any other value.

 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
   it is available.

 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.

 * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
   container with a tmpfs, but leave the directory from the image in place.

 systemd-logind:

 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
   hibernation is available even if the swap devices do not provide enough room
   for it.

 systemd-udevd:

 * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
   "v238", "v239", "v240"…, or the special value "latest") as parameter. If
   specified udev's net_id builtin will follow the specified naming scheme when
   determining stable network interface names. This may be used to revert to
   naming schemes of older udev versions, in order to provide more stable naming
   across updates. This environment variable takes precedence over the kernel
   command line option `net.naming-scheme=`, except if the value is prefixed
   with `:` in which case the kernel command line option takes precedence, if it
   is specified as well.

 installed systemd tests:

 * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
   a test executable is moved to an arbitrary location.

 nss-systemd:

 * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
   user/group records for the `root` and `nobody` users if they are missing from
   `/etc/passwd`.

 * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
   user/group records for dynamically registered service users (i.e. users
   registered through `DynamicUser=1`).

 * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
   dynamic user lookups. This is primarily useful to make `nss-systemd` work
   safely from within `dbus-daemon`.

 systemd-timedated:

 * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
   NTP client services. If set, `timedatectl set-ntp on` enables and starts the
   first existing unit listed in the environment variable, and
   `timedatectl set-ntp off` disables and stops all listed units.

 systemd-sulogin-shell:

 * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
   root password is not available (such as when the root account is locked).
   See `sulogin(8)` for more details.

 bootctl and other tools that access the EFI System Partition (ESP):

 * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
   relaxed. Specifically, validation checks that ensure the specified ESP path
   is a FAT file system are turned off, as are checks that the path is located
   on a GPT partition with the correct type UUID.

 * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
   may be used to override ESP path auto detection, and redirect any accesses to
   the ESP to the specified directory. Not that unlike with bootctl's --path=
   switch only very superficial validation of the specified path is done when
   this environment variable is used.

 systemd itself:

 * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
   are done by the service manager on behalf of a specific unit, in child
   processes that are later (after execve()) going to become unit
   processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
   modules can use this information to determine in which context and on whose
   behalf they are being called, which may be useful to avoid deadlocks, for
   example to bypass IPC calls to the very service that is about to be
   started. Note that NSS and PAM modules should be careful to only rely on this
   data when invoked privileged, or possibly only when getppid() returns 1, as
   setting environment variables is of course possible in any even unprivileged
   contexts.

 * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
   it is either set to `system` or `user` depending on whether the NSS/PAM
   module is called by systemd in `--system` or `--user` mode.

 systemd-remount-fs:

 * `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory
   exists in /etc/fstab (this file always takes precedence), then the root
   directory is remounted writable. This is primarily used by
   systemd-gpt-auto-generator to ensure the root partition is mounted writable
   in accordance to the GPT partition flags.
	---
	title: Known Environment Variables
	---

	# Known Environment Variables

	A number of systemd components take additional runtime parameters via
	environment variables. Many of these environment variables are not supported at
	the same level as command line switches and other interfaces are: we don't
	document them in the man pages and we make no stability guarantees for
	them. While they generally are unlikely to be dropped any time soon again, we
	do not want to guarantee that they stay around for good either.

	Below is an (incomprehensive) list of the environment variables understood by
	the various tools. Note that this list only covers environment variables not
	documented in the proper man pages.

	All tools:

	* `$SYSTEMD_OFFLINE=[0\|1]` — if set to `1`, then `systemctl` will
	refrain from talking to PID 1; this has the same effect as the historical
	detection of `chroot()`. Setting this variable to `0` instead has a similar
	effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
	communicate with PID 1 even if a `chroot()` environment is detected.
	You almost certainly want to set this to `1` if you maintain a package build system
	or similar and are trying to use a modern container system and not plain
	`chroot()`.

	* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
	`chroot()` environment. This is particularly relevant for systemctl, as it
	will not alter its behaviour for `chroot()` environments if set. Normally it
	refrains from talking to PID 1 in such a case; turning most operations such
	as `start` into no-ops. If that's what's explicitly desired, you might
	consider setting `SYSTEMD_OFFLINE=1`.

	* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
	will print latency information at runtime.

	* `$SYSTEMD_PROC_CMDLINE` — if set, may contain a string that is used as kernel
	command line instead of the actual one readable from /proc/cmdline. This is
	useful for debugging, in order to test generators and other code against
	specific kernel command lines.

	* `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
	This is useful for debugging and testing initrd-only programs in the main
	system.

	* `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
	completion. If no time unit is specified, assumes seconds. The usual other units
	are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
	to 0, then the built-in default is used.

	* `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
	hash tables is turned off, and libc malloc() is used for all allocations.

	* `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
	not output graphical smiley emojis, but ASCII alternatives instead. Note that
	this only controls use of Unicode emoji glyphs, and has no effect on other
	Unicode glyphs.

	systemctl:

	* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
	listener, and instead always connect through the dbus-daemon D-bus broker.

	* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
	the client side, instead of asking PID 1 to do this.

	* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.

	systemd-nspawn:

	* `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
	hierarchy mode.

	* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
	friends writable in the container. If set to "network", leave only
	/proc/sys/net writable.

	* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
	uses to register with machined. If unset defaults to "nspawn", but with this
	variable may be set to any other value.

	* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
	it is available.

	* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.

	* `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
	container with a tmpfs, but leave the directory from the image in place.

	systemd-logind:

	* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
	hibernation is available even if the swap devices do not provide enough room
	for it.

	systemd-udevd:

	* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
	"v238", "v239", "v240"…, or the special value "latest") as parameter. If
	specified udev's net_id builtin will follow the specified naming scheme when
	determining stable network interface names. This may be used to revert to
	naming schemes of older udev versions, in order to provide more stable naming
	across updates. This environment variable takes precedence over the kernel
	command line option `net.naming-scheme=`, except if the value is prefixed
	with `:` in which case the kernel command line option takes precedence, if it
	is specified as well.

	installed systemd tests:

	* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
	a test executable is moved to an arbitrary location.

	nss-systemd:

	* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
	user/group records for the `root` and `nobody` users if they are missing from
	`/etc/passwd`.

	* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
	user/group records for dynamically registered service users (i.e. users
	registered through `DynamicUser=1`).

	* `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
	dynamic user lookups. This is primarily useful to make `nss-systemd` work
	safely from within `dbus-daemon`.

	systemd-timedated:

	* `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
	NTP client services. If set, `timedatectl set-ntp on` enables and starts the
	first existing unit listed in the environment variable, and
	`timedatectl set-ntp off` disables and stops all listed units.

	systemd-sulogin-shell:

	* `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
	root password is not available (such as when the root account is locked).
	See `sulogin(8)` for more details.

	bootctl and other tools that access the EFI System Partition (ESP):

	* `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
	relaxed. Specifically, validation checks that ensure the specified ESP path
	is a FAT file system are turned off, as are checks that the path is located
	on a GPT partition with the correct type UUID.

	* `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
	may be used to override ESP path auto detection, and redirect any accesses to
	the ESP to the specified directory. Not that unlike with bootctl's --path=
	switch only very superficial validation of the specified path is done when
	this environment variable is used.

	systemd itself:

	* `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
	are done by the service manager on behalf of a specific unit, in child
	processes that are later (after execve()) going to become unit
	processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
	modules can use this information to determine in which context and on whose
	behalf they are being called, which may be useful to avoid deadlocks, for
	example to bypass IPC calls to the very service that is about to be
	started. Note that NSS and PAM modules should be careful to only rely on this
	data when invoked privileged, or possibly only when getppid() returns 1, as
	setting environment variables is of course possible in any even unprivileged
	contexts.

	* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
	it is either set to `system` or `user` depending on whether the NSS/PAM
	module is called by systemd in `--system` or `--user` mode.

	systemd-remount-fs:

	* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory
	exists in /etc/fstab (this file always takes precedence), then the root
	directory is remounted writable. This is primarily used by
	systemd-gpt-auto-generator to ensure the root partition is mounted writable
	in accordance to the GPT partition flags.