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diff --git a/docs/ENVIRONMENT.md b/docs/ENVIRONMENT.md new file mode 100644 index 0000000000..619a57eb3f --- /dev/null +++ b/docs/ENVIRONMENT.md @@ -0,0 +1,175 @@ +# Known Environment Variables + +A number of systemd components take additional runtime parameters via +environment variables. Many of these environment variables are not supported at +the same level as command line switches and other interfaces are: we don't +document them in the man pages and we make no stability guarantees for +them. While they generally are unlikely to be dropped any time soon again, we +do not want to guarantee that they stay around for good either. + +Below is an (incomprehensive) list of the environment variables understood by +the various tools. Note that this list only covers environment variables not +documented in the proper man pages. + +All tools: + +* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will + refrain from talking to PID 1; this has the same effect as the historical + detection of `chroot()`. Setting this variable to `0` instead has a similar + effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to + communicate with PID 1 even if a `chroot()` environment is detected. + You almost certainly want to set this to `1` if you maintain a package build system + or similar and are trying to use a modern container system and not plain + `chroot()`. + +* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a + `chroot()` environment. This is particularly relevant for systemctl, as it + will not alter its behaviour for `chroot()` environments if set. Normally it + refrains from talking to PID 1 in such a case; turning most operations such + as `start` into no-ops. If that's what's explicitly desired, you might + consider setting `SYSTEMD_OFFLINE=1`. + +* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation + will print latency information at runtime. + +* `$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. + +* `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection. + This is useful for debugging and testing initrd-only programs in the main + system. + +* `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call + completion. If no time unit is specified, assumes seconds. The usual other units + 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. + +* `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by + hash tables is turned off, and libc malloc() is used for all allocations. + +* `$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: + +* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus + listener, and instead always connect through the dbus-daemon D-bus broker. + +* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on + the client side, instead of asking PID 1 to do this. + +* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks. + +systemd-nspawn: + +* `$UNIFIED_CGROUP_HIERARCHY=1` — if set, force nspawn into unified cgroup + hierarchy mode. + +* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and + friends writable in the container. If set to "network", leave only + /proc/sys/net writable. + +* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn + uses to register with machined. If unset defaults to "nspawn", but with this + variable may be set to any other value. + +* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if + it is available. + +* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running. + +* `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the + container with a tmpfs, but leave the directory from the image in place. + +systemd-logind: + +* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that + hibernation is available even if the swap devices do not provide enough room + for it. + +systemd-udevd: + +* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of + "v238", "v239", "v240"…, or the special value "latest") as parameter. If + specified udev's net_id builtin will follow the specified naming scheme when + determining stable network interface names. This may be used to revert to + naming schemes of older udev versions, in order to provide more stable naming + across updates. This environment variable takes precedence over the kernel + command line option `net.naming-scheme=`, except if the value is prefixed + with `:` in which case the kernel command line option takes precedence, if it + is specified as well. + +installed systemd tests: + +* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if + a test executable is moved to an arbitrary location. + +nss-systemd: + +* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize + user/group records for the `root` and `nobody` users if they are missing from + `/etc/passwd`. + +* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return + user/group records for dynamically registered service users (i.e. users + registered through `DynamicUser=1`). + +* `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do + dynamic user lookups. This is primarily useful to make `nss-systemd` work + safely from within `dbus-daemon`. + +systemd-timedated: + +* `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of + NTP client services. If set, `timedatectl set-ntp on` enables and starts the + first existing unit listed in the environment variable, and + `timedatectl set-ntp off` disables and stops all listed units. + +systemd-sulogin-shell: + +* `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the + root password is not available (such as when the root account is locked). + See `sulogin(8)` for more details. + +bootctl and other tools that access the EFI System Partition (ESP): + +* `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are + relaxed. Specifically, validation checks that ensure the specified ESP path + 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 + are done by the service manager on behalf of a specific unit, in child + processes that are later (after execve()) going to become unit + processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM + modules can use this information to determine in which context and on whose + behalf they are being called, which may be useful to avoid deadlocks, for + example to bypass IPC calls to the very service that is about to be + started. Note that NSS and PAM modules should be careful to only rely on this + data when invoked privileged, or possibly only when getppid() returns 1, as + setting environment variables is of course possible in any even unprivileged + contexts. + +* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$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. |