This adds $SYSTEMD_SYSROOT_FSTAB analoguous to $SYSTEMD_FSTAB.
22 KiB
title | category | layout | SPDX-License-Identifier |
---|---|---|---|
Known Environment Variables | Interfaces | default | LGPL-2.1-or-later |
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:
-
$SYSTEMD_OFFLINE=[0|1]
— if set to1
, thensystemctl
will refrain from talking to PID 1; this has the same effect as the historical detection ofchroot()
. Setting this variable to0
instead has a similar effect as$SYSTEMD_IGNORE_CHROOT=1
; i.e. tools will try to communicate with PID 1 even if achroot()
environment is detected. You almost certainly want to set this to1
if you maintain a package build system or similar and are trying to use a modern container system and not plainchroot()
. -
$SYSTEMD_IGNORE_CHROOT=1
— if set, don't check whether being invoked in achroot()
environment. This is particularly relevant for systemctl, as it will not alter its behaviour forchroot()
environments if set. Normally it refrains from talking to PID 1 in such a case; turning most operations such asstart
into no-ops. If that's what's explicitly desired, you might consider setting$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, 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 taken relative to the outside 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 debuggingsystemd-fstab-generator
. -
$SYSTEMD_CRYPTTAB
— if set, use this path instead of/etc/crypttab
. Only useful for debugging. Currently only supported bysystemd-cryptsetup-generator
. -
$SYSTEMD_INTEGRITYTAB
— if set, use this path instead of/etc/integritytab
. Only useful for debugging. Currently only supported bysystemd-integritysetup-generator
. -
$SYSTEMD_VERITYTAB
— if set, use this path instead of/etc/veritytab
. Only useful for debugging. Currently only supported bysystemd-veritysetup-generator
. -
$SYSTEMD_EFI_OPTIONS
— if set, used instead of the string in theSystemdOptions
EFI variable. Analogous to$SYSTEMD_PROC_CMDLINE
. -
$SYSTEMD_DEFAULT_HOSTNAME
— override the compiled-in fallback hostname (relevant in particular for the system manager andsystemd-hostnamed
). Must be a valid hostname (either a single label or a FQDN). -
$SYSTEMD_IN_INITRD=[auto|lenient|0|1]
— if set, specifies initrd detection method. Defaults toauto
. Behavior is defined as follows:auto
: Checks if/etc/initrd-release
exists, and a temporary fs is mounted on/
. If both conditions meet, then it's in initrd.lenient
: Similar toauto
, but the rootfs check is skipped.0|1
: Simply 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 libcmalloc()
is used for all allocations. -
$SYSTEMD_EMOJI=0
— if set, tools such assystemd-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 whenRuntimeDirectory=
is used, see systemd.exec(5). -
$SYSTEMD_CRYPT_PREFIX
— if set configures the hash method prefix to use for UNIXcrypt()
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, internalcrypt()
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 insystemd-nspawn
, will be logged to the audit log, if the kernel supports this.
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.
systemd-nspawn
:
-
$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1
— if set, forcesystemd-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_SUPPRESS_SYNC=1
— if set, all disk synchronization syscalls are blocked to the container payload (e.g.sync()
,fsync()
,syncfs()
, …) and theO_SYNC
/O_DSYNC
flags are made unavailable toopen()
and friends. This is equivalent to passing--suppress-sync=yes
on thesystemd-nspawn
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, overridessystemd-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 ofsystemd-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 ofsystemd-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 withsystemd-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'snet_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 optionnet.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.
nss-systemd
:
-
$SYSTEMD_NSS_BYPASS_SYNTHETIC=1
— if set,nss-systemd
won't synthesize user/group records for theroot
andnobody
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 throughDynamicUser=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, andtimedatectl 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). Seesulogin(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 withbootctl
'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 tosystem
oruser
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 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 bysystemd-gpt-auto-generator
to ensure the root partition is mounted writable in accordance to the GPT partition flags.
systemd-firstboot
and localectl
:
$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-sysext
:
$SYSTEMD_SYSEXT_HIERARCHIES
— this variable may be used to override which hierarchies are managed bysystemd-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.
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 to1
(or another value interpreted as true), these lines will always create subvolumes if the backing filesystem supports them. If set to0
, these lines will always create directories.
systemd-sysv-generator
:
-
$SYSTEMD_SYSVINIT_PATH
— Controls wheresystemd-sysv-generator
looks for SysV init scripts. -
$SYSTEMD_SYSVRCND_PATH
— Controls wheresystemd-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.
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_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-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 bysystemd-cryptsetup
. Defaults to enabled.
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 secondarysystemd-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 secondarysystemd-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 tosystemd-homed
's D-Bus and Varlink service names/sockets. This is also understood byhomectl
. This too is useful for running an additional copy ofsystemd-homed
that doesn't interfere with the host's main one. -
$SYSTEMD_HOMEWORK_PATH
– configures the path to thesystemd-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.
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.