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08b04ec7e7
This adds the support for veritytab. The veritytab file contains at most five fields, the first four are mandatory, the last one is optional: - The first field contains the name of the resulting verity volume; its block device is set up /dev/mapper/</filename>. - The second field contains a path to the underlying block data device, or a specification of a block device via UUID= followed by the UUID. - The third field contains a path to the underlying block hash device, or a specification of a block device via UUID= followed by the UUID. - The fourth field is the roothash in hexadecimal. - The fifth field, if present, is a comma-delimited list of options. The following options are recognized only: ignore-corruption, restart-on-corruption, panic-on-corruption, ignore-zero-blocks, check-at-most-once and root-hash-signature. The others options will be implemented later. Also, this adds support for the new kernel verity command line boolean option "veritytab" which enables the read for veritytab, and the new environment variable SYSTEMD_VERITYTAB which sets the path to the file veritytab to read.
266 lines
13 KiB
Markdown
266 lines
13 KiB
Markdown
---
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title: Known Environment Variables
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category: Interfaces
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layout: default
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---
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# Known Environment Variables
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A number of systemd components take additional runtime parameters via
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environment variables. Many of these environment variables are not supported at
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the same level as command line switches and other interfaces are: we don't
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document them in the man pages and we make no stability guarantees for
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them. While they generally are unlikely to be dropped any time soon again, we
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do not want to guarantee that they stay around for good either.
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Below is an (incomprehensive) list of the environment variables understood by
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the various tools. Note that this list only covers environment variables not
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documented in the proper man pages.
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All tools:
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* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
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refrain from talking to PID 1; this has the same effect as the historical
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detection of `chroot()`. Setting this variable to `0` instead has a similar
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effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
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communicate with PID 1 even if a `chroot()` environment is detected.
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You almost certainly want to set this to `1` if you maintain a package build system
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or similar and are trying to use a modern container system and not plain
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`chroot()`.
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* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
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`chroot()` environment. This is particularly relevant for systemctl, as it
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will not alter its behaviour for `chroot()` environments if set. Normally it
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refrains from talking to PID 1 in such a case; turning most operations such
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as `start` into no-ops. If that's what's explicitly desired, you might
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consider setting `SYSTEMD_OFFLINE=1`.
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* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
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will print latency information at runtime.
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* `$SYSTEMD_PROC_CMDLINE` — if set, the contents are used as the kernel command
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line instead of the actual one in /proc/cmdline. This is useful for
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debugging, in order to test generators and other code against specific kernel
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command lines.
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* `$SYSTEMD_FSTAB` — if set, use this path instead of /etc/fstab. Only useful
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for debugging.
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* `$SYSTEMD_CRYPTTAB` — if set, use this path instead of /etc/crypttab. Only
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useful for debugging. Currently only supported by systemd-cryptsetup-generator.
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* `$SYSTEMD_VERITYTAB` — if set, use this path instead of /etc/veritytab. Only
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useful for debugging. Currently only supported by systemd-veritysetup-generator.
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* `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in the
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SystemdOptions EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
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* `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
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This is useful for debugging and testing initrd-only programs in the main
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system.
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* `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
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completion. If no time unit is specified, assumes seconds. The usual other units
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are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
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to 0, then the built-in default is used.
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* `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
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hash tables is turned off, and libc malloc() is used for all allocations.
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* `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
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not output graphical smiley emojis, but ASCII alternatives instead. Note that
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this only controls use of Unicode emoji glyphs, and has no effect on other
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Unicode glyphs.
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* `$RUNTIME_DIRECTORY` — various tools use this variable to locate the
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appropriate path under /run. This variable is also set by the manager when
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RuntimeDirectory= is used, see systemd.exec(5).
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* `$SYSTEMD_CRYPT_PREFIX` — if set configures the hash method prefix to use for
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UNIX crypt() when generating passwords. By default the system's "preferred
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method" is used, but this can be overridden with this environment
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variable. Takes a prefix such as `$6$` or `$y$`. (Note that this is only
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honoured on systems built with libxcrypt and is ignored on systems using
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glibc's original, internal crypt() implementation.)
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* `$SYSTEMD_RDRAND=0` — if set, the RDRAND instruction will never be used,
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even if the CPU supports it.
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* `$SYSTEMD_SECCOMP=0` – if set, seccomp filters will not be enforced, even if
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support for it is compiled in and available in the kernel.
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* `$SYSTEMD_LOG_SECCOMP=1` — if set, system calls blocked by seccomp filtering,
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for example in systemd-nspawn, will be logged to the audit log, if the current
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kernel version supports this.
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systemctl:
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* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID1's private D-Bus
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listener, and instead always connect through the dbus-daemon D-bus broker.
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* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
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the client side, instead of asking PID 1 to do this.
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* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
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systemd-nspawn:
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* `$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1` — if set, force nspawn into unified
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cgroup hierarchy mode.
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* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make /sys and /proc/sys and
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friends writable in the container. If set to "network", leave only
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/proc/sys/net writable.
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* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
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uses to register with machined. If unset defaults to "nspawn", but with this
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variable may be set to any other value.
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* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
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it is available.
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* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
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* `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount /tmp in the
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container with a tmpfs, but leave the directory from the image in place.
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systemd-logind:
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* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
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hibernation is available even if the swap devices do not provide enough room
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for it.
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systemd-udevd:
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* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
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"v238", "v239", "v240"…, or the special value "latest") as parameter. If
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specified udev's net_id builtin will follow the specified naming scheme when
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determining stable network interface names. This may be used to revert to
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naming schemes of older udev versions, in order to provide more stable naming
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across updates. This environment variable takes precedence over the kernel
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command line option `net.naming-scheme=`, except if the value is prefixed
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with `:` in which case the kernel command line option takes precedence, if it
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is specified as well.
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* `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set overrides systemd-logind's
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built-in EFI logic of requesting a reboot into the firmware. Takes a
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boolean. If set to false the functionality is turned off entirely. If set to
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true instead of requesting a reboot into the firmware setup UI through EFI a
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file `/run/systemd/reboot-to-firmware-setup` is created whenever this is
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requested. This file may be checked for by services run during system
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shutdown in order to request the appropriate operation from the firmware in
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an alternative fashion.
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* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows
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overriding of systemd-logind's built-in EFI logic of requesting a reboot into
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the boot loader menu. Takes a boolean. If set to false the functionality is
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turned off entirely. If set to true instead of requesting a reboot into the
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boot loader menu through EFI a file `/run/systemd/reboot-to-boot-loader-menu`
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is created whenever this is requested. The file contains the requested boot
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loader menu timeout in µs, formatted in ASCII decimals, or zero in case no
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timeout is requested. This file may be checked for by services run during
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system shutdown in order to request the appropriate operation from the boot
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loader in an alternative fashion.
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* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows
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overriding of systemd-logind's built-in EFI logic of requesting a reboot into
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a specific boot loader entry. Takes a boolean. If set to false the
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functionality is turned off entirely. If set to true instead of requesting a
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reboot into a specific boot loader entry through EFI a file
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`/run/systemd/reboot-to-boot-loader-entry` is created whenever this is
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requested. The file contains the requested boot loader entry identifier. This
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file may be checked for by services run during system shutdown in order to
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request the appropriate operation from the boot loader in an alternative
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fashion. Note that by default only boot loader entries which follow the [Boot
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Loader Specification](https://systemd.io/BOOT_LOADER_SPECIFICATION) and are
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placed in the ESP or the Extended Boot Loader partition may be selected this
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way. However, if a directory `/run/boot-loader-entries/` exists, the entries
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are loaded from there instead. The directory should contain the usual
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directory hierarchy mandated by the Boot Loader Specification, i.e. the entry
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drop-ins should be placed in
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`/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by
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the drop-ins (including the kernels and initrds) somewhere else below
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`/run/boot-loader-entries/`. Note that all these files may be (and are
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supposed to be) symlinks. systemd-logind will load these files on-demand,
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these files can hence be updated (ideally atomically) whenever the boot
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loader configuration changes. A foreign boot loader installer script should
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hence synthesize drop-in snippets and symlinks for all boot entries at boot
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or whenever they change if it wants to integrate with systemd-logind's APIs.
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installed systemd tests:
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* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
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a test executable is moved to an arbitrary location.
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nss-systemd:
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* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
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user/group records for the `root` and `nobody` users if they are missing from
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`/etc/passwd`.
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* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
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user/group records for dynamically registered service users (i.e. users
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registered through `DynamicUser=1`).
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* `$SYSTEMD_NSS_BYPASS_BUS=1` — if set, `nss-systemd` won't use D-Bus to do
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dynamic user lookups. This is primarily useful to make `nss-systemd` work
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safely from within `dbus-daemon`.
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systemd-timedated:
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* `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
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NTP client services. If set, `timedatectl set-ntp on` enables and starts the
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first existing unit listed in the environment variable, and
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`timedatectl set-ntp off` disables and stops all listed units.
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systemd-sulogin-shell:
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* `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
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root password is not available (such as when the root account is locked).
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See `sulogin(8)` for more details.
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bootctl and other tools that access the EFI System Partition (ESP):
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* `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
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relaxed. Specifically, validation checks that ensure the specified ESP path
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is a FAT file system are turned off, as are checks that the path is located
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on a GPT partition with the correct type UUID.
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* `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
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may be used to override ESP path auto detection, and redirect any accesses to
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the ESP to the specified directory. Not that unlike with bootctl's --path=
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switch only very superficial validation of the specified path is done when
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this environment variable is used.
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systemd itself:
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* `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
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are done by the service manager on behalf of a specific unit, in child
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processes that are later (after execve()) going to become unit
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processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
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modules can use this information to determine in which context and on whose
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behalf they are being called, which may be useful to avoid deadlocks, for
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example to bypass IPC calls to the very service that is about to be
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started. Note that NSS and PAM modules should be careful to only rely on this
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data when invoked privileged, or possibly only when getppid() returns 1, as
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setting environment variables is of course possible in any even unprivileged
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contexts.
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* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
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it is either set to `system` or `user` depending on whether the NSS/PAM
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module is called by systemd in `--system` or `--user` mode.
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systemd-remount-fs:
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* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and no entry for the root directory
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exists in /etc/fstab (this file always takes precedence), then the root
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directory is remounted writable. This is primarily used by
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systemd-gpt-auto-generator to ensure the root partition is mounted writable
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in accordance to the GPT partition flags.
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systemd-firstboot and localectl:
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* `SYSTEMD_LIST_NON_UTF8_LOCALES=1` – if set non-UTF-8 locales are listed among
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the installed ones. By default non-UTF-8 locales are suppressed from the
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selection, since we are living in the 21st century.
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