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_IN_CHROOT=0; 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_IN_CHROOT=0|1 — takes a boolean. If set, overrides chroot detection.
This is particularly relevant for systemctl, as it will not alter its behaviour
for chroot() environments if SYSTEMD_IN_CHROOT=0. 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.
$SYSTEMD_FIRST_BOOT=0|1 — if set, assume “first boot” condition to be false
or true, instead of checking the flag file created by PID 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, the contents are used as the kernel command
line instead of the actual one in /proc/cmdline. This is useful for
debugging, in order to test generators and other code against specific kernel
command lines.
$SYSTEMD_OS_RELEASE — if set, use this path instead of /etc/os-release or
/usr/lib/os-release. When operating under some root (e.g. systemctl
--root=…), the path is prefixed with the root. Only useful for debugging.
$SYSTEMD_FSTAB — if set, use this path instead of /etc/fstab. Only useful
for debugging.
$SYSTEMD_SYSROOT_FSTAB — if set, use this path instead of
/sysroot/etc/fstab. Only useful for debugging systemd-fstab-generator.
$SYSTEMD_SYSFS_CHECK — takes a boolean. If set, overrides sysfs container
detection that ignores /dev/ entries in fstab. Only useful for debugging
systemd-fstab-generator.
$SYSTEMD_CRYPTTAB — if set, use this path instead of /etc/crypttab. Only
useful for debugging. Currently only supported by
systemd-cryptsetup-generator.
$SYSTEMD_INTEGRITYTAB — if set, use this path instead of
/etc/integritytab. Only useful for debugging. Currently only supported by
systemd-integritysetup-generator.
$SYSTEMD_VERITYTAB — if set, use this path instead of
/etc/veritytab. Only useful for debugging. Currently only supported by
systemd-veritysetup-generator.
$SYSTEMD_EFI_OPTIONS — if set, used instead of the string in the
SystemdOptions EFI variable. Analogous to $SYSTEMD_PROC_CMDLINE.
$SYSTEMD_DEFAULT_HOSTNAME — override the compiled-in fallback hostname
(relevant in particular for the system manager and systemd-hostnamed).
Must be a valid hostname (either a single label or a FQDN).
$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_UTF8= — takes a boolean value, and overrides whether to generate
non-ASCII special glyphs at various places (i.e. “→” instead of
“->”). Usually this is determined automatically, based on $LC_CTYPE, but in
scenarios where locale definitions are not installed it might make sense to
override this check explicitly.
$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.
$RUNTIME_DIRECTORY — various tools use this variable to locate the
appropriate path under /run/. This variable is also set by the manager when
RuntimeDirectory= is used, see systemd.exec(5).
$SYSTEMD_CRYPT_PREFIX — if set configures the hash method prefix to use for
UNIX crypt() when generating passwords. By default the system’s “preferred
method” is used, but this can be overridden with this environment variable.
Takes a prefix such as $6$ or $y$. (Note that this is only honoured on
systems built with libxcrypt and is ignored on systems using glibc’s
original, internal crypt() implementation.)
$SYSTEMD_SECCOMP=0 — if set, seccomp filters will not be enforced, even if
support for it is compiled in and available in the kernel.
$SYSTEMD_LOG_SECCOMP=1 — if set, system calls blocked by seccomp filtering,
for example in systemd-nspawn, will be logged to the audit log, if the
kernel supports this.
$SYSTEMD_ENABLE_LOG_CONTEXT — if set, extra fields will always be logged to
the journal instead of only when logging in debug mode.
$SYSTEMD_NETLINK_DEFAULT_TIMEOUT — specifies the default timeout of waiting
replies for netlink messages from the kernel. Defaults to 25 seconds.
$SYSTEMD_VERITY_SHARING=0 — if set, sharing dm-verity devices by
using a stable <ROOTHASH>-verity device mapper name will be disabled.
systemctl:
$SYSTEMCTL_FORCE_BUS=1 — if set, do not connect to PID 1’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 SysV compatibility hooks.
$SYSTEMCTL_SKIP_AUTO_KEXEC=1 — if set, do not automatically kexec instead of
reboot when a new kernel has been loaded.
$SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT=1 — if set, do not automatically soft-reboot
instead of reboot when a new root file system has been loaded in
/run/nextroot/.
systemd-nspawn:
$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1 — if set, force systemd-nspawn into
unified cgroup hierarchy mode.
$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1 — if set, make /sys/, /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_NSPAWN_CHECK_OS_RELEASE=0 — if set, do not fail when trying to
boot an OS tree without an os-release file (useful when trying to boot a
container with empty /etc/ and bind-mounted /usr/)
$SYSTEMD_SUPPRESS_SYNC=1 — if set, all disk synchronization syscalls are
blocked to the container payload (e.g. sync(), fsync(), syncfs(), …)
and the O_SYNC/O_DSYNC flags are made unavailable to open() and
friends. This is equivalent to passing --suppress-sync=yes on the
systemd-nspawn command line.
$SYSTEMD_NSPAWN_NETWORK_MAC=... — if set, allows users to set a specific MAC
address for a container, ensuring that it uses the provided value instead of
generating a random one. It is effective when used with --network-veth. The
expected format is six groups of two hexadecimal digits separated by colons,
e.g. SYSTEMD_NSPAWN_NETWORK_MAC=12:34:56:78:90:AB
systemd-vmspawn:
$SYSTEMD_VMSPAWN_NETWORK_MAC=... — if set, allows users to set a specific MAC
address for a VM, ensuring that it uses the provided value instead of
generating a random one. It is effective when used with --network-tap. The
expected format is six groups of two hexadecimal digits separated by colons,
e.g. SYSTEMD_VMSPAWN_NETWORK_MAC=12:34:56:78:90:AB
$SYSTEMD_VMSPAWN_QEMU_EXTRA=… – may contain additional command line
arguments to append the qemu command line.
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_REBOOT_TO_FIRMWARE_SETUP — if set, overrides systemd-logind’s
built-in EFI logic of requesting a reboot into the firmware. Takes a boolean.
If set to false, the functionality is turned off entirely. If set to true,
instead of requesting a reboot into the firmware setup UI through EFI a file,
/run/systemd/reboot-to-firmware-setup is created whenever this is
requested. This file may be checked for by services run during system
shutdown in order to request the appropriate operation from the firmware in
an alternative fashion.
$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU — similar to the above, allows
overriding of systemd-logind’s built-in EFI logic of requesting a reboot
into the boot loader menu. Takes a boolean. If set to false, the
functionality is turned off entirely. If set to true, instead of requesting a
reboot into the boot loader menu through EFI, the file
/run/systemd/reboot-to-boot-loader-menu is created whenever this is
requested. The file contains the requested boot loader menu timeout in µs,
formatted in ASCII decimals, or zero in case no timeout is requested. This
file may be checked for by services run during system shutdown in order to
request the appropriate operation from the boot loader in an alternative
fashion.
$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY — similar to the above, allows
overriding of systemd-logind’s built-in EFI logic of requesting a reboot
into a specific boot loader entry. Takes a boolean. If set to false, the
functionality is turned off entirely. If set to true, instead of requesting a
reboot into a specific boot loader entry through EFI, the file
/run/systemd/reboot-to-boot-loader-entry is created whenever this is
requested. The file contains the requested boot loader entry identifier. This
file may be checked for by services run during system shutdown in order to
request the appropriate operation from the boot loader in an alternative
fashion. Note that by default only boot loader entries which follow the
Boot Loader Specification
and are placed in the ESP or the Extended Boot Loader partition may be
selected this way. However, if a directory /run/boot-loader-entries/
exists, the entries are loaded from there instead. The directory should
contain the usual directory hierarchy mandated by the Boot Loader
Specification, i.e. the entry drop-ins should be placed in
/run/boot-loader-entries/loader/entries/*.conf, and the files referenced by
the drop-ins (including the kernels and initrds) somewhere else below
/run/boot-loader-entries/. Note that all these files may be (and are
supposed to be) symlinks. systemd-logind will load these files on-demand,
these files can hence be updated (ideally atomically) whenever the boot
loader configuration changes. A foreign boot loader installer script should
hence synthesize drop-in snippets and symlinks for all boot entries at boot
or whenever they change if it wants to integrate with systemd-logind’s
APIs.
systemd-udevd and sd-device library:
$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.
$SYSTEMD_DEVICE_VERIFY_SYSFS — if set to “0”, disables verification that
devices sysfs path are actually backed by sysfs. Relaxing this verification
is useful for testing purposes.
$SYSTEMD_UDEV_EXTRA_TIMEOUT_SEC= — Specifies an extra timespan that the
udev manager process waits for a worker process kills slow programs specified
by IMPORT{program}=, PROGRAM=, or RUN=, and finalizes the processing event.
If the worker process cannot finalize the event within the specified timespan,
the worker process is killed by the manager process. Defaults to 10 seconds,
maximum allowed is 5 hours.
udevadm and systemd-hwdb:
SYSTEMD_HWDB_UPDATE_BYPASS= — If set to “1”, execution of hwdb updates is skipped
when udevadm hwdb --update or systemd-hwdb update are invoked. This can
be useful if either of these tools are invoked unconditionally as a child
process by another tool, such as package managers running either of these
tools in a postinstall script.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-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. Note that unlike with bootctl’s
--path= switch only very superficial validation of the specified path is
done when this environment variable is used.
$KERNEL_INSTALL_CONF_ROOT=… — override the built in default configuration
directory /etc/kernel/ to read files like entry-token and install.conf from.
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_SUPPORT_DEVICE, $SYSTEMD_SUPPORT_MOUNT, $SYSTEMD_SUPPORT_SWAP -
can be set to 0 to mark respective unit type as unsupported. Generally,
having less units saves system resources so these options might be useful
for cases where we don’t need to track given unit type, e.g. --user manager
often doesn’t need to deal with device or swap units because they are
handled by the --system manager (PID 1). Note that setting certain unit
type as unsupported might not prevent loading some units of that type if they
are referenced by other units of another supported type.
$SYSTEMD_DEFAULT_MOUNT_RATE_LIMIT_BURST — can be set to override the mount
units burst rate limit for parsing /proc/self/mountinfo. On a system with
few resources but many mounts the rate limit may be hit, which will cause the
processing of mount units to stall. The burst limit may be adjusted when the
default is not appropriate for a given system. Defaults to 5, accepts
positive integers.
systemd-remount-fs:
$SYSTEMD_REMOUNT_ROOT_RW=1 — if set 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.systemd-firstboot, localectl, and systemd-localed:
$SYSTEMD_LIST_NON_UTF8_LOCALES=1 — if set, non-UTF-8 locales are listed among
the installed ones. By default non-UTF-8 locales are suppressed from the
selection, since we are living in the 21st century.
$SYSTEMD_KEYMAP_DIRECTORIES= — takes a colon (:) separated list of keymap
directories. The directories must be absolute and normalized. If unset, the
default keymap directories (/usr/share/keymaps/, /usr/share/kbd/keymaps/, and
/usr/lib/kbd/keymaps/) will be used.
systemd-resolved:
$SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME — if set to “0”, systemd-resolved
won’t synthesize A/AAAA/PTR RRs for the system hostname on either regular nor
reverse lookups.systemd-sysext:
$SYSTEMD_SYSEXT_HIERARCHIES — this variable may be used to override which
hierarchies are managed by systemd-sysext. By default only /usr/ and
/opt/ are managed, and directories may be added or removed to that list by
setting this environment variable to a colon-separated list of absolute
paths. Only “real” file systems and directories that only contain “real” file
systems as submounts should be used. Do not specify API file systems such as
/proc/ or /sys/ here, or hierarchies that have them as submounts. In
particular, do not specify the root directory / here. Similarly,
$SYSTEMD_CONFEXT_HIERARCHIES works for confext images and supports the
systemd-confext multi-call functionality of sysext.
$SYSTEMD_SYSEXT_MUTABLE_MODE — this variable may be used to override the
default mutability mode for hierarchies managed by systemd-sysext. It takes
the same values the --mutable= command line switch does. Note that the
command line still overrides the effect of the environment
variable. Similarly, $SYSTEMD_CONFEXT_MUTABLE_MODE works for confext images
and supports the systemd-confext multi-call functionality of sysext.
systemd-tmpfiles:
$SYSTEMD_TMPFILES_FORCE_SUBVOL — if unset, v/q/Q lines will create
subvolumes only if the OS itself is installed into a subvolume. If set to 1
(or another value interpreted as true), these lines will always create
subvolumes if the backing filesystem supports them. If set to 0, these
lines will always create directories.systemd-sysusers
$SOURCE_DATE_EPOCH — if unset, the field of the date of last password change
in /etc/shadow will be the number of days from Jan 1, 1970 00:00 UTC until
today. If $SOURCE_DATE_EPOCH is set to a valid UNIX epoch value in seconds,
then the field will be the number of days until that time instead. This is to
support creating bit-by-bit reproducible system images by choosing a
reproducible value for the field of the date of last password change in
/etc/shadow. See: https://reproducible-builds.org/specs/source-date-epoch/systemd-sysv-generator:
$SYSTEMD_SYSVINIT_PATH — Controls where systemd-sysv-generator looks for
SysV init scripts.
$SYSTEMD_SYSVRCND_PATH — Controls where systemd-sysv-generator looks for
SysV init script runlevel link farms.
systemd tests:
$SYSTEMD_TEST_DATA — override the location of test data. This is useful if
a test executable is moved to an arbitrary location.
$SYSTEMD_TEST_NSS_BUFSIZE — size of scratch buffers for “reentrant”
functions exported by the nss modules.
$TESTFUNCS – takes a colon separated list of test functions to invoke,
causes all non-matching test functions to be skipped. Only applies to tests
using our regular test boilerplate.
fuzzers:
$SYSTEMD_FUZZ_OUTPUT — A boolean that specifies whether to write output to
stdout. Setting to true is useful in manual invocations, since all output is
suppressed by default.
$SYSTEMD_FUZZ_RUNS — The number of times execution should be repeated in
manual invocations.
Note that it may be also useful to set $SYSTEMD_LOG_LEVEL, since all logging
is suppressed by default.
systemd-importd:
$SYSTEMD_IMPORT_BTRFS_SUBVOL — takes a boolean, which controls whether to
prefer creating btrfs subvolumes over plain directories for machine
images. Has no effect on non-btrfs file systems where subvolumes are not
available anyway. If not set, defaults to true.
$SYSTEMD_IMPORT_BTRFS_QUOTA — takes a boolean, which controls whether to set
up quota automatically for created btrfs subvolumes for machine images. If
not set, defaults to true. Has no effect if machines are placed in regular
directories, because btrfs subvolumes are not supported or disabled. If
enabled, the quota group of the subvolume is automatically added to a
combined quota group for all such machine subvolumes.
$SYSTEMD_IMPORT_SYNC — takes a boolean, which controls whether to
synchronize images to disk after installing them, before completing the
operation. If not set, defaults to true. If disabled installation of images
will be quicker, but not as safe.
systemd-dissect, systemd-nspawn and all other tools that may operate on
disk images with --image= or similar:
$SYSTEMD_DISSECT_VERITY_SIDECAR — takes a boolean, which controls whether to
load “sidecar” Verity metadata files. If enabled (which is the default),
whenever a disk image is used, a set of files with the .roothash,
.usrhash, .roothash.p7s, .usrhash.p7s, .verity suffixes are searched
adjacent to disk image file, containing the Verity root hashes, their
signatures or the Verity data itself. If disabled this automatic discovery of
Verity metadata files is turned off.
$SYSTEMD_DISSECT_VERITY_EMBEDDED — takes a boolean, which controls whether
to load the embedded Verity signature data. If enabled (which is the
default), Verity root hash information and a suitable signature is
automatically acquired from a signature partition, following the
Discoverable Partitions Specification.
If disabled any such partition is ignored. Note that this only disables
discovery of the root hash and its signature, the Verity data partition
itself is still searched in the GPT image.
$SYSTEMD_DISSECT_VERITY_SIGNATURE — takes a boolean, which controls whether
to validate the signature of the Verity root hash if available. If enabled
(which is the default), the signature of suitable disk images is validated
against any of the certificates in /etc/verity.d/*.crt (and similar
directories in /usr/lib/, /run, …) or passed to the kernel for validation
against its built-in certificates.
$SYSTEMD_DISSECT_VERITY_TIMEOUT_SEC=sec — takes a timespan, which controls
the timeout waiting for the image to be configured. Defaults to 100 msec.
$SYSTEMD_DISSECT_FILE_SYSTEMS= — takes a colon-separated list of file
systems that may be mounted for automatically dissected disk images. If not
specified defaults to something like: ext4:btrfs:xfs:vfat:erofs:squashfs
$SYSTEMD_LOOP_DIRECT_IO – takes a boolean, which controls whether to enable
LO_FLAGS_DIRECT_IO (i.e. direct IO + asynchronous IO) on loopback block
devices when opening them. Defaults to on, set this to “0” to disable this
feature.
$SYSTEMD_ALLOW_USERSPACE_VERITY — takes a boolean, which controls whether
to consider the userspace Verity public key store in /etc/verity.d/ (and
related directories) to authenticate signatures on Verity hashes of disk
images. Defaults to true, i.e. userspace signature validation is allowed. If
false, authentication can be done only via the kernel’s internal keyring.
systemd-cryptsetup:
$SYSTEMD_CRYPTSETUP_USE_TOKEN_MODULE – takes a boolean, which controls
whether to use the libcryptsetup “token” plugin module logic even when
activating via FIDO2, PKCS#11, TPM2, i.e. mechanisms natively supported by
systemd-cryptsetup. Defaults to enabled.
$SYSTEMD_CRYPTSETUP_TOKEN_PATH – takes a path to a directory in the file
system. If specified overrides where libcryptsetup will look for token
modules (.so). This is useful for debugging token modules: set this
environment variable to the build directory and you are set. This variable
is only supported when systemd is compiled in developer mode.
Various tools that read passwords from the TTY, such as systemd-cryptenroll
and homectl:
$PASSWORD — takes a string: the literal password to use. If this
environment variable is set it is used as password instead of prompting the
user interactively. This exists primarily for debugging and testing
purposes. Do not use this for production code paths, since environment
variables are typically inherited down the process tree without restrictions
and should thus not be used for secrets.
$NEWPASSWORD — similar to $PASSWORD above, but is used when both a
current and a future password are required, for example if the password is to
be changed. In that case $PASSWORD shall carry the current (i.e. old)
password and $NEWPASSWORD the new.
systemd-homed:
$SYSTEMD_HOME_ROOT – defines an absolute path where to look for home
directories/images. When unspecified defaults to /home/. This is useful for
debugging purposes in order to run a secondary systemd-homed instance that
operates on a different directory where home directories/images are placed.
$SYSTEMD_HOME_RECORD_DIR – defines an absolute path where to look for
fixated home records kept on the host. When unspecified defaults to
/var/lib/systemd/home/. Similar to $SYSTEMD_HOME_ROOT this is useful for
debugging purposes, in order to run a secondary systemd-homed instance that
operates on a record database entirely separate from the host’s.
$SYSTEMD_HOME_DEBUG_SUFFIX – takes a short string that is suffixed to
systemd-homed’s D-Bus and Varlink service names/sockets. This is also
understood by homectl. This too is useful for running an additional copy of
systemd-homed that doesn’t interfere with the host’s main one.
$SYSTEMD_HOMEWORK_PATH – configures the path to the systemd-homework
binary to invoke. If not specified defaults to
/usr/lib/systemd/systemd-homework.
Combining these four environment variables is pretty useful when
debugging/developing systemd-homed:
SYSTEMD_HOME_DEBUG_SUFFIX=foo \
SYSTEMD_HOMEWORK_PATH=/home/lennart/projects/systemd/build/systemd-homework \
SYSTEMD_HOME_ROOT=/home.foo/ \
SYSTEMD_HOME_RECORD_DIR=/var/lib/systemd/home.foo/ \
/home/lennart/projects/systemd/build/systemd-homed
$SYSTEMD_HOME_MOUNT_OPTIONS_BTRFS, $SYSTEMD_HOME_MOUNT_OPTIONS_EXT4,
$SYSTEMD_HOME_MOUNT_OPTIONS_XFS – configure the default mount options to
use for LUKS home directories, overriding the built-in default mount
options. There’s one variable for each of the supported file systems for the
LUKS home directory backend.
$SYSTEMD_HOME_MKFS_OPTIONS_BTRFS, $SYSTEMD_HOME_MKFS_OPTIONS_EXT4,
$SYSTEMD_HOME_MKFS_OPTIONS_XFS – configure additional arguments to use for
mkfs when formatting LUKS home directories. There’s one variable for each
of the supported file systems for the LUKS home directory backend.
$SYSTEMD_HOME_LOCK_FREEZE_SESSION - Takes a boolean. When false, the user’s
session will not be frozen when the home directory is locked. Note that the kernel
may still freeze any task that tries to access data from the user’s locked home
directory. This can lead to data loss, security leaks, or other undesired behavior
caused by parts of the session becoming unresponsive due to disk I/O while other
parts of the session continue running. Thus, we highly recommend that this variable
isn’t used unless necessary. Defaults to true.
kernel-install:
$KERNEL_INSTALL_BYPASS – If set to “1”, execution of kernel-install is skipped
when kernel-install is invoked. This can be useful if kernel-install is invoked
unconditionally as a child process by another tool, such as package managers
running kernel-install in a postinstall script.systemd-journald, journalctl:
$SYSTEMD_JOURNAL_COMPACT – Takes a boolean. If enabled, journal files are written
in a more compact format that reduces the amount of disk space required by the
journal. Note that journal files in compact mode are limited to 4G to allow use of
32-bit offsets. Enabled by default.
$SYSTEMD_JOURNAL_COMPRESS – Takes a boolean, or one of the compression
algorithms “XZ”, “LZ4”, and “ZSTD”. If enabled, the default compression
algorithm set at compile time will be used when opening a new journal file.
If disabled, the journal file compression will be disabled. Note that the
compression mode of existing journal files are not changed. To make the
specified algorithm takes an effect immediately, you need to explicitly run
journalctl --rotate.
$SYSTEMD_CATALOG – path to the compiled catalog database file to use for
journalctl -x, journalctl --update-catalog, journalctl --list-catalog
and related calls.
$SYSTEMD_CATALOG_SOURCES – path to the catalog database input source
directory to use for journalctl --update-catalog.
systemd-pcrextend, systemd-cryptsetup:
$SYSTEMD_FORCE_MEASURE=1 — If set, force measuring of resources (which are
marked for measurement) even if not booted on a kernel equipped with
systemd-stub. Normally, requested measurement of resources is conditionalized
on kernels that have booted with systemd-stub. With this environment
variable the test for that my be bypassed, for testing purposes.systemd-repart:
$SYSTEMD_REPART_MKFS_OPTIONS_<FSTYPE> – configure additional arguments to use for
mkfs when formatting partition file systems. There’s one variable for each
of the supported file systems.
$SYSTEMD_REPART_OVERRIDE_FSTYPE – if set the value will override the file
system type specified in Format= lines in partition definition files.
Additionally, the filesystem for all partitions with a specific designator can
be overridden via a correspondingly named environment variable. For example,
to override the filesystem type for all partitions with Type=root, you can
set SYSTEMD_REPART_OVERRIDE_FSTYPE_ROOT=ext4.
systemd-nspawn, systemd-networkd:
$SYSTEMD_FIREWALL_BACKEND – takes a string, either iptables or
nftables. Selects the firewall backend to use. If not specified tries to
use nftables and falls back to iptables if that’s not available.systemd-networkd:
$SYSTEMD_NETWORK_PERSISTENT_STORAGE_READY – takes a boolean. If true,
systemd-networkd tries to open the persistent storage on start. To make this
work, ProtectSystem=strict in systemd-networkd.service needs to be downgraded
or disabled.systemd-storagetm:
$SYSTEMD_NVME_MODEL, $SYSTEMD_NVME_FIRMWARE, $SYSTEMD_NVME_SERIAL,
$SYSTEMD_NVME_UUID – these take a model string, firmware version string,
serial number string, and UUID formatted as string. If specified these
override the defaults exposed on the NVME subsystem and namespace, which are
derived from the underlying block device and system identity. Do not set the
latter two via the environment variable unless systemd-storagetm is invoked
to expose a single device only, since those identifiers better should be kept
unique.systemd-pcrlock, systemd-pcrextend:
$SYSTEMD_MEASURE_LOG_USERSPACE – the path to the tpm2-measure.log file
(containing userspace measurement data) to read. This allows overriding the
default of /run/log/systemd/tpm2-measure.log.
$SYSTEMD_MEASURE_LOG_FIRMWARE – the path to the binary_bios_measurements
file (containing firmware measurement data) to read. This allows overriding
the default of /sys/kernel/security/tpm0/binary_bios_measurements.
systemd-sleep:
$SYSTEMD_SLEEP_FREEZE_USER_SESSIONS - Takes a boolean. When true (the default),
user.slice will be frozen during sleep. When false it will not be. We recommend
against using this variable, because it can lead to undesired behavior, especially
for systems that use home directory encryption and for
systemd-suspend-then-hibernate.service.Tools using the Varlink protocol (such as varlinkctl) or sd-bus (such as
busctl):
$SYSTEMD_SSH – the ssh binary to invoke when the ssh: transport is
used. May be a filename (which is searched for in $PATH) or absolute path.
$SYSTEMD_VARLINK_LISTEN – interpreted by some tools that provide a Varlink
service. Takes a file system path: if specified the tool will listen on an
AF_UNIX stream socket on the specified path in addition to whatever else it
would listen on.
systemd-mountfsd:
$SYSTEMD_MOUNTFSD_TRUSTED_DIRECTORIES – takes a boolean argument. If true
disk images from the usual disk image directories (/var/lib/machines/,
/var/lib/confexts/, …) will be considered “trusted”, i.e. are validated
with a more relaxed image policy (typically not requiring Verity signature
checking) than those from other directories (where Verity signature checks
are mandatory). If false all images are treated the same, regardless if
placed in the usual disk image directories or elsewhere. If not set defaults
to a compile time setting.
$SYSTEMD_MOUNTFSD_IMAGE_POLICY_TRUSTED,
$SYSTEMD_MOUNTFSD_IMAGE_POLICY_UNTRUSTED – the default image policy to
apply to trusted and untrusted disk images. An image is considered trusted if
placed in a trusted disk image directory (see above), or if suitable polkit
authentication was acquired. See systemd.image-policy(7) for the valid
syntax for image policy strings.
systemd-run, run0, systemd-nspawn, systemd-vmspawn:
$SYSTEMD_TINT_BACKGROUND – Takes a boolean. When false the automatic
tinting of the background for containers, VMs, and interactive systemd-run
and run0 invocations is turned off. Note that this environment variable has
no effect if the background color is explicitly selected via the relevant
--background= switch of the tool.
$SYSTEMD_ADJUST_TERMINAL_TITLE – Takes a boolean. When false the terminal
window title will not be updated for interactive invocation of the mentioned
tools.