+---
+title: Known Environment Variables
+---
+
# Known Environment Variables
A number of systemd components take additional runtime parameters via
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.
-* `$SYSTEMD_MEMPOOL=0` — if set the internal memory caching logic employed by
+* `$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
hibernation is available even if the swap devices do not provide enough room
for it.
+systemd-udevd:
+
+* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
+ "v238", "v239", "v240"…, or the special value "latest") as parameter. If
+ specified udev's net_id builtin will follow the specified naming scheme when
+ determining stable network interface names. This may be used to revert to
+ naming schemes of older udev versions, in order to provide more stable naming
+ across updates. This environment variable takes precedence over the kernel
+ command line option `net.naming-scheme=`, except if the value is prefixed
+ with `:` in which case the kernel command line option takes precedence, if it
+ is specified as well.
+
+* `$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.
+
+* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows
+ overriding of systemd-logind's built-in EFI logic of requesting a reboot into
+ the boot loader menu. Takes a boolean. If set to false the functionality is
+ turned off entirely. If set to true instead of requesting a reboot into the
+ boot loader menu through EFI a file `/run/systemd/reboot-to-boot-loader-menu`
+ is created whenever this is requested. The file contains the requested boot
+ loader menu timeout in µs, formatted in ASCII decimals, or zero in case no
+ time-out is requested. This file may be checked for by services run during
+ system shutdown in order to request the appropriate operation from the boot
+ loader in an alternative fashion.
+
+* `$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:
* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
is a FAT file system are turned off, as are checks that the path is located
on a GPT partition with the correct type UUID.
+* `$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:
* `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
* `$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.
projects / thirdparty / systemd.git / blobdiff