docs/ENVIRONMENT.md

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