docs/ENVIRONMENT.md

   1 ---
   2 title: Known Environment Variables
   3 category: Interfaces
   4 ---
   5
   6 # Known Environment Variables
   7
   8 A number of systemd components take additional runtime parameters via
   9 environment variables. Many of these environment variables are not supported at
  10 the same level as command line switches and other interfaces are: we don't
  11 document them in the man pages and we make no stability guarantees for
  12 them. While they generally are unlikely to be dropped any time soon again, we
  13 do not want to guarantee that they stay around for good either.
  14
  15 Below is an (incomprehensive) list of the environment variables understood by
  16 the various tools. Note that this list only covers environment variables not
  17 documented in the proper man pages.
  18
  19 All tools:
  20
  21 * `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
  22   refrain from talking to PID 1; this has the same effect as the historical
  23   detection of `chroot()`.  Setting this variable to `0` instead has a similar
  24   effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
  25   communicate with PID 1 even if a `chroot()` environment is detected.
  26   You almost certainly want to set this to `1` if you maintain a package build system
  27   or similar and are trying to use a modern container system and not plain
  28   `chroot()`.
  29
  30 * `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
  31   `chroot()` environment. This is particularly relevant for systemctl, as it
  32   will not alter its behaviour for `chroot()` environments if set.  Normally it
  33   refrains from talking to PID 1 in such a case; turning most operations such
  34   as `start` into no-ops.  If that's what's explicitly desired, you might
  35   consider setting `SYSTEMD_OFFLINE=1`.
  36
  37 * `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
  38   will print latency information at runtime.
  39
  40 * `$SYSTEMD_PROC_CMDLINE` — if set, the contents are used as the kernel command
  41   line instead of the actual one in /proc/cmdline. This is useful for
  42   debugging, in order to test generators and other code against specific kernel
  43   command lines.
  44
  45 * `$SYSTEMD_FSTAB` — if set, use this path instead of /etc/fstab. Only useful
  46   for debugging.
  47
  48 * `$SYSTEMD_CRYPTTAB` — if set, use this path instead of /etc/crypttab. Only
  49   useful for debugging. Currently only supported by systemd-cryptsetup-generator.
  50
  51 * `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in the
  52   SystemdOptions EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
  53
  54 * `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
  55   This is useful for debugging and testing initrd-only programs in the main
  56   system.
  57
  58 * `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
  59   completion. If no time unit is specified, assumes seconds. The usual other units
  60   are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
  61   to 0, then the built-in default is used.
  62
  63 * `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
  64   hash tables is turned off, and libc malloc() is used for all allocations.
  65
  66 * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
  67   not output graphical smiley emojis, but ASCII alternatives instead. Note that
  68   this only controls use of Unicode emoji glyphs, and has no effect on other
  69   Unicode glyphs.
  70
  71 * `$RUNTIME_DIRECTORY` — various tools use this variable to locate the
  72   appropriate path under /run. This variable is also set by the manager when
  73   RuntimeDirectory= is used, see systemd.exec(5).
  74
  75 systemctl:
  76
  77 * `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
  78   listener, and instead always connect through the dbus-daemon D-bus broker.
  79
  80 * `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
  81   the client side, instead of asking PID 1 to do this.
  82
  83 * `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
  84
  85 systemd-nspawn:
  86
  87 * `$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1` — if set, force nspawn into unified
  88   cgroup hierarchy mode.
  89
  90 * `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
  91   friends writable in the container. If set to "network", leave only
  92   /proc/sys/net writable.
  93
  94 * `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
  95   uses to register with machined. If unset defaults to "nspawn", but with this
  96   variable may be set to any other value.
  97
  98 * `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
  99   it is available.
 100
 101 * `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
 102
 103 * `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
 104   container with a tmpfs, but leave the directory from the image in place.
 105
 106 systemd-logind:
 107
 108 * `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
 109   hibernation is available even if the swap devices do not provide enough room
 110   for it.
 111
 112 systemd-udevd:
 113
 114 * `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
 115   "v238", "v239", "v240"…, or the special value "latest") as parameter. If
 116   specified udev's net_id builtin will follow the specified naming scheme when
 117   determining stable network interface names. This may be used to revert to
 118   naming schemes of older udev versions, in order to provide more stable naming
 119   across updates. This environment variable takes precedence over the kernel
 120   command line option `net.naming-scheme=`, except if the value is prefixed
 121   with `:` in which case the kernel command line option takes precedence, if it
 122   is specified as well.
 123
 124 * `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set overrides systemd-logind's
 125   built-in EFI logic of requesting a reboot into the firmware. Takes a
 126   boolean. If set to false the functionality is turned off entirely. If set to
 127   true instead of requesting a reboot into the firmware setup UI through EFI a
 128   file `/run/systemd/reboot-to-firmware-setup` is created whenever this is
 129   requested. This file may be checked for by services run during system
 130   shutdown in order to request the appropriate operation from the firmware in
 131   an alternative fashion.
 132
 133 * `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows
 134   overriding of systemd-logind's built-in EFI logic of requesting a reboot into
 135   the boot loader menu. Takes a boolean. If set to false the functionality is
 136   turned off entirely. If set to true instead of requesting a reboot into the
 137   boot loader menu through EFI a file `/run/systemd/reboot-to-boot-loader-menu`
 138   is created whenever this is requested. The file contains the requested boot
 139   loader menu timeout in µs, formatted in ASCII decimals, or zero in case no
 140   time-out is requested. This file may be checked for by services run during
 141   system shutdown in order to request the appropriate operation from the boot
 142   loader in an alternative fashion.
 143
 144 * `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows
 145   overriding of systemd-logind's built-in EFI logic of requesting a reboot into
 146   a specific boot loader entry. Takes a boolean. If set to false the
 147   functionality is turned off entirely. If set to true instead of requesting a
 148   reboot into a specific boot loader entry through EFI a file
 149   `/run/systemd/reboot-to-boot-loader-entry` is created whenever this is
 150   requested. The file contains the requested boot loader entry identifier. This
 151   file may be checked for by services run during system shutdown in order to
 152   request the appropriate operation from the boot loader in an alternative
 153   fashion. Note that by default only boot loader entries which follow the [Boot
 154   Loader Specification](https://systemd.io/BOOT_LOADER_SPECIFICATION) and are
 155   placed in the ESP or the Extended Boot Loader partition may be selected this
 156   way. However, if a directory `/run/boot-loader-entries/` exists, the entries
 157   are loaded from there instead. The directory should contain the usual
 158   directory hierarchy mandated by the Boot Loader Specification, i.e. the entry
 159   drop-ins should be placed in
 160   `/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by
 161   the drop-ins (including the kernels and initrds) somewhere else below
 162   `/run/boot-loader-entries/`. Note that all these files may be (and are
 163   supposed to be) symlinks. systemd-logind will load these files on-demand,
 164   these files can hence be updated (ideally atomically) whenever the boot
 165   loader configuration changes. A foreign boot loader installer script should
 166   hence synthesize drop-in snippets and symlinks for all boot entries at boot
 167   or whenever they change if it wants to integrate with systemd-logind's APIs.
 168
 169 installed systemd tests:
 170
 171 * `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
 172   a test executable is moved to an arbitrary location.
 173
 174 nss-systemd:
 175
 176 * `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
 177   user/group records for the `root` and `nobody` users if they are missing from
 178   `/etc/passwd`.
 179
 180 * `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
 181   user/group records for dynamically registered service users (i.e. users
 182   registered through `DynamicUser=1`).
 183
 184 * `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
 185   dynamic user lookups. This is primarily useful to make `nss-systemd` work
 186   safely from within `dbus-daemon`.
 187
 188 systemd-timedated:
 189
 190 * `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
 191   NTP client services. If set, `timedatectl set-ntp on` enables and starts the
 192   first existing unit listed in the environment variable, and
 193   `timedatectl set-ntp off` disables and stops all listed units.
 194
 195 systemd-sulogin-shell:
 196
 197 * `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
 198   root password is not available (such as when the root account is locked).
 199   See `sulogin(8)` for more details.
 200
 201 bootctl and other tools that access the EFI System Partition (ESP):
 202
 203 * `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
 204   relaxed. Specifically, validation checks that ensure the specified ESP path
 205   is a FAT file system are turned off, as are checks that the path is located
 206   on a GPT partition with the correct type UUID.
 207
 208 * `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
 209   may be used to override ESP path auto detection, and redirect any accesses to
 210   the ESP to the specified directory. Not that unlike with bootctl's --path=
 211   switch only very superficial validation of the specified path is done when
 212   this environment variable is used.
 213
 214 systemd itself:
 215
 216 * `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
 217   are done by the service manager on behalf of a specific unit, in child
 218   processes that are later (after execve()) going to become unit
 219   processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
 220   modules can use this information to determine in which context and on whose
 221   behalf they are being called, which may be useful to avoid deadlocks, for
 222   example to bypass IPC calls to the very service that is about to be
 223   started. Note that NSS and PAM modules should be careful to only rely on this
 224   data when invoked privileged, or possibly only when getppid() returns 1, as
 225   setting environment variables is of course possible in any even unprivileged
 226   contexts.
 227
 228 * `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
 229   it is either set to `system` or `user` depending on whether the NSS/PAM
 230   module is called by systemd in `--system` or `--user` mode.
 231
 232 systemd-remount-fs:
 233
 234 * `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and no entry for the root directory
 235   exists in /etc/fstab (this file always takes precedence), then the root
 236   directory is remounted writable. This is primarily used by
 237   systemd-gpt-auto-generator to ensure the root partition is mounted writable
 238   in accordance to the GPT partition flags.
 239
 240 systemd-firstboot and localectl:
 241
 242 * `SYSTEMD_LIST_NON_UTF8_LOCALES=1` – if set non-UTF-8 locales are listed among
 243   the installed ones. By default non-UTF-8 locales are suppressed from the
 244   selection, since we are living in the 21st century.