---
title: Known Environment Variables
+category: Interfaces
---
# 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.
+* `$RUNTIME_DIRECTORY` — various tools use this variable to locate the
+ appropriate path under /run. This variable is also set by the manager when
+ RuntimeDirectory= is used, see systemd.exec(5).
+
systemctl:
* `$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
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.