---
title: Known Environment Variables
+category: Interfaces
+layout: default
---
# Known Environment Variables
* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
will print latency information at runtime.
-* `$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.
+* `$SYSTEMD_PROC_CMDLINE` — if set, the contents are used as the kernel command
+ line instead of the actual one in /proc/cmdline. This is useful for
+ debugging, in order to test generators and other code against specific kernel
+ command lines.
+
+* `$SYSTEMD_FSTAB` — if set, use this path instead of /etc/fstab. Only useful
+ for debugging.
+
+* `$SYSTEMD_CRYPTTAB` — if set, use this path instead of /etc/crypttab. Only
+ useful for debugging. Currently only supported by systemd-cryptsetup-generator.
+
+* `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in the
+ SystemdOptions EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
* `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
This is useful for debugging and testing initrd-only programs in the main
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.)
+
systemctl:
* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
systemd-nspawn:
-* `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup
- hierarchy mode.
+* `$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1` — if set, force nspawn into unified
+ cgroup hierarchy mode.
* `$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
with `:` in which case the kernel command line option takes precedence, if it
is specified as well.
+* `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set overrides systemd-logind's
+ built-in EFI logic of requesting a reboot into the firmware. Takes a
+ boolean. If set to false the functionality is turned off entirely. If set to
+ true instead of requesting a reboot into the firmware setup UI through EFI a
+ file `/run/systemd/reboot-to-firmware-setup` is created whenever this is
+ requested. This file may be checked for by services run during system
+ shutdown in order to request the appropriate operation from the firmware in
+ an alternative fashion.
+
+* `$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 a 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.
+
+* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows
+ overriding of systemd-logind's built-in EFI logic of requesting a reboot into
+ a specific boot loader entry. Takes a boolean. If set to false the
+ functionality is turned off entirely. If set to true instead of requesting a
+ reboot into a specific boot loader entry through EFI a file
+ `/run/systemd/reboot-to-boot-loader-entry` is created whenever this is
+ requested. The file contains the requested boot loader entry identifier. This
+ file may be checked for by services run during system shutdown in order to
+ request the appropriate operation from the boot loader in an alternative
+ fashion. Note that by default only boot loader entries which follow the [Boot
+ Loader Specification](https://systemd.io/BOOT_LOADER_SPECIFICATION) and are
+ placed in the ESP or the Extended Boot Loader partition may be selected this
+ way. However, if a directory `/run/boot-loader-entries/` exists, the entries
+ are loaded from there instead. The directory should contain the usual
+ directory hierarchy mandated by the Boot Loader Specification, i.e. the entry
+ drop-ins should be placed in
+ `/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by
+ the drop-ins (including the kernels and initrds) somewhere else below
+ `/run/boot-loader-entries/`. Note that all these files may be (and are
+ supposed to be) symlinks. systemd-logind will load these files on-demand,
+ these files can hence be updated (ideally atomically) whenever the boot
+ loader configuration changes. A foreign boot loader installer script should
+ hence synthesize drop-in snippets and symlinks for all boot entries at boot
+ or whenever they change if it wants to integrate with systemd-logind's APIs.
+
installed systemd tests:
* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
systemd-remount-fs:
-* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory
+* `$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 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.
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