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docs: add a "front matter" snippet to our markdown pages It turns out Jekyll (the engine behind GitHub Pages) requires that pages include a "Front Matter" snippet of YAML at the top for proper rendering. Omitting it will still render the pages, but including it opens up new possibilities, such as using a {% for %} loop to generate index.md instead of requiring a separate script. I'm hoping this will also fix the issue with some of the pages (notably CODE_OF_CONDUCT.html) not being available under systemd.io Tested locally by rendering the website with Jekyll. Before this change, the *.md files were kept unchanged (so not sure how that even works?!), after this commit, proper *.html files were generated from it.
2019-01-03 01:16:34 +03:00
---
title: Known Environment Variables
---
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
# 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:
systemctl,verbs: Introduce SYSTEMD_OFFLINE environment variable A lot of code references the `running_in_chroot()` function; while I didn't dig I'm pretty certain this arose to deal with situations like RPM package builds in `mock` - there we don't want the `%post`s to `systemctl start` for example. And actually this exact same use case arises for [rpm-ostree](https://github.com/projectatomic/rpm-ostree/) where we implement offline upgrades by default; the `%post`s are always run in a new chroot using [bwrap](https://github.com/projectatomic/bubblewrap). And here's the problem: bwrap creates proper mount roots, so it passes `running_in_chroot()`, and then if a script tries to do `systemctl start` we get: `System has not been booted with systemd as init system (PID 1)` but that's an *error*, unlike the `running_in_chroot()` case where we ignore. Further complicating things is there are real world RPM packages like `glusterfs` which end up invoking `systemctl start`. A while ago, the `SYSTEMD_IGNORE_CHROOT` environment variable was added for the inverse case of running in a chroot, but still wanting to use systemd as PID 1 (presumably some broken initramfs setups?). Let's introduce a `SYSTEMD_OFFLINE` environment variable for cases like mock/rpm-ostree so we can force on the "ignore everything except preset" logic. This way we'll still not start services even if mock switches to use nspawn or bwrap or something else that isn't a chroot. We also cleanly supercede the `SYSTEMD_IGNORE_CHROOT=1` which is now spelled `SYSTEMD_OFFLINE=0`. (Suggested by @poettering) Also I made things slightly nicer here and we now print the ignored operation.
2017-12-14 00:04:41 +03:00
* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will
refrain from talking to PID 1; this has the same effect as the historical
detection of `chroot()`. Setting this variable to `0` instead has a similar
effect as `SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to
communicate with PID 1 even if a `chroot()` environment is detected.
You almost certainly want to set this to `1` if you maintain a package build system
or similar and are trying to use a modern container system and not plain
`chroot()`.
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
systemctl,verbs: Introduce SYSTEMD_OFFLINE environment variable A lot of code references the `running_in_chroot()` function; while I didn't dig I'm pretty certain this arose to deal with situations like RPM package builds in `mock` - there we don't want the `%post`s to `systemctl start` for example. And actually this exact same use case arises for [rpm-ostree](https://github.com/projectatomic/rpm-ostree/) where we implement offline upgrades by default; the `%post`s are always run in a new chroot using [bwrap](https://github.com/projectatomic/bubblewrap). And here's the problem: bwrap creates proper mount roots, so it passes `running_in_chroot()`, and then if a script tries to do `systemctl start` we get: `System has not been booted with systemd as init system (PID 1)` but that's an *error*, unlike the `running_in_chroot()` case where we ignore. Further complicating things is there are real world RPM packages like `glusterfs` which end up invoking `systemctl start`. A while ago, the `SYSTEMD_IGNORE_CHROOT` environment variable was added for the inverse case of running in a chroot, but still wanting to use systemd as PID 1 (presumably some broken initramfs setups?). Let's introduce a `SYSTEMD_OFFLINE` environment variable for cases like mock/rpm-ostree so we can force on the "ignore everything except preset" logic. This way we'll still not start services even if mock switches to use nspawn or bwrap or something else that isn't a chroot. We also cleanly supercede the `SYSTEMD_IGNORE_CHROOT=1` which is now spelled `SYSTEMD_OFFLINE=0`. (Suggested by @poettering) Also I made things slightly nicer here and we now print the ignored operation.
2017-12-14 00:04:41 +03:00
`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`.
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
will print latency information at runtime.
Add support for SystemdOptions EFI var to augment /proc/cmdline In various circumstances, overriding the kernel commandline can be inconvenient. People have different bootloaders, and e.g. the grub config can be pretty scary. grubby helps, but it isn't always available. This option adds an alternative mechanism that can quite convenient on EFI systems. cmdline settings have higher priority, because they can be (usually) changed on the bootloader prompt. $SYSTEMD_EFI_OPTIONS can be used to override, same as $SYSTEMD_PROC_CMDLINE.
2019-08-01 16:33:35 +03:00
* `$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.
cryptsetup-generator: allow overriding crypttab path with $SYSTEMD_CRYPTAB
2019-11-13 12:31:44 +03:00
* `$SYSTEMD_CRYPTTAB` — if set, use this path instead of /etc/crypttab. Only
useful for debugging. Currently only supported by systemd-cryptsetup-generator.
Add support for SystemdOptions EFI var to augment /proc/cmdline In various circumstances, overriding the kernel commandline can be inconvenient. People have different bootloaders, and e.g. the grub config can be pretty scary. grubby helps, but it isn't always available. This option adds an alternative mechanism that can quite convenient on EFI systems. cmdline settings have higher priority, because they can be (usually) changed on the bootloader prompt. $SYSTEMD_EFI_OPTIONS can be used to override, same as $SYSTEMD_PROC_CMDLINE.
2019-08-01 16:33:35 +03:00
* `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in SystemdOptions
EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
util-lib: read $SYSTEMD_PROC_CMDLINE if set when looking for the kernel cmdline if we want to parse the kernel command line, let's check the $SYSTEMD_PROC_CMDLINE environment variable first. This is useful for debugging purposes.
2016-12-12 15:42:06 +03:00
Add $SYSTEMD_IN_INITRD=yes|no override for debugging
2018-09-26 08:15:55 +03:00
* `$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.
sd-bus: make BUS_DEFAULT_TIMEOUT configurable This adds sd_bus_{get,set}_method_call_timeout(). If the timeout is not set or set to 0, then the timeout value is parsed from $SYSTEMD_BUS_TIMEOUT= environment variable. If the environment variable is not set, then built-in timeout is used.
2018-07-13 11:38:47 +03:00
* `$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.
locale-util: add logic to output smiley emojis at various happiness levels
2018-11-06 19:59:58 +03:00
* `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
hashmap: add an environment variable to turn off the memory pool used by hashmaps Triggered by https://bugzilla.redhat.com/show_bug.cgi?id=1609349
2018-08-03 17:45:21 +03:00
hash tables is turned off, and libc malloc() is used for all allocations.
locale-util: add logic to output smiley emojis at various happiness levels
2018-11-06 19:59:58 +03:00
* `$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.
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
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.
* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call out to SysV compatibility hooks.
systemd-nspawn:
nspawn: rename UNIFIED_CGROUP_HIERARCHY to SYSTEMD_NSPAWN_UNIFIED_HIERARCHY We should never have used an unprefixed environment variable name. All other systemd-nspawn variables have the "SYSTEMD_NSPAWN_" prefix, and all other systemd variables have the "SYSTEMD_" prefix. The new variable name takes precedence, but we fall back to checking the old one. If only the old one is found, a warning is emitted. In addition, SYSTEMD_NSPAWN_UNIFIED_HIERARCHY="" is accepted as an override to avoid looking for the old variable name. We have a variable with the same name ($UNIFIED_CGROUP_HIERARCHY) in tests, which governs both systemd-nspawn and qemu behaviour. It is not renamed.
2019-09-27 15:17:41 +03:00
* `$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1` — if set, force nspawn into unified
cgroup hierarchy mode.
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
* `$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.
* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
nspawn: optionally don't mount a tmpfs over /tmp (#10294) nspawn: optionally, don't mount a tmpfs on /tmp Fixes: #10260
2018-10-08 19:32:03 +03:00
* `$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.
Add a bit of documentation for the various undocumented environment variables we honour
2016-11-24 19:47:39 +03:00
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.
Rename $TEST_DIR to $SYSTEMD_TEST_DATA, document it TEST_DIR is rather generic, and we prefix all variables used by installed executables with "SYSTEMD_".
2017-02-15 03:17:38 +03:00
docs: add missing section to ENVIRONMENT.md No, this is not an env var understood by logind. Let's fix the confusoin.
2018-12-17 18:37:18 +03:00
systemd-udevd:
udev: introduce udev net_id "naming schemes" With this we can stabilize how naming works for network interfaces. A user can request through a kernel cmdline option or an env var which scheme to follow. The idea is that installers use this to set into stone (a very soft stone though) the scheme used during installation so that interface naming doesn't change afterwards anymore. Why use env vars and kernel cmdline options, and not a config file of its own? Well, first of all there's no obvious existing one to use. But more importantly: I have the feeling that this logic is kind of an incomplete hack, and I simply don't want to do advertise this as a perfectly working solution. So far we used env vars for the non-so-official options and proper config files for the official stuff. Given how incomplete this logic is (i.e. the big variable for naming remains the kernel, which might expose sysfs attributes in newer versions that we check for and didn't exist in older versions — and other problems like this), I am simply not confident in giving this first-class exposure in a primary configuration file. Fixes: #10448
2018-12-10 19:10:19 +03:00
* `$NET_NAMING_SCHEME=` – if set, takes a network naming scheme (i.e. one of
meson: make net.naming-scheme= default configurable This is useful for distributions, where the stability of interface names should be preseved after an upgrade of systemd. So when some specific release of the distro is made available, systemd defaults to the latest & greatest naming scheme, and subsequent updates set the same default. This default may still be overriden through the kernel and env var options. A special value "latest" is also allowed. Without a specific name, it is harder to verride from meson. In case of 'combo' options, meson reads the default during the initial configuration, and "remembers" this choice. When systemd is updated, old build/ directories could keep the old default, which would be annoying. Hence, "latest" is introduced to make it explicit, yet follow the upstream. This is actually useful for the user too, because it may be used as an override, without having to actually specify a version.
2018-12-12 01:28:29 +03:00
"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.
udev: introduce udev net_id "naming schemes" With this we can stabilize how naming works for network interfaces. A user can request through a kernel cmdline option or an env var which scheme to follow. The idea is that installers use this to set into stone (a very soft stone though) the scheme used during installation so that interface naming doesn't change afterwards anymore. Why use env vars and kernel cmdline options, and not a config file of its own? Well, first of all there's no obvious existing one to use. But more importantly: I have the feeling that this logic is kind of an incomplete hack, and I simply don't want to do advertise this as a perfectly working solution. So far we used env vars for the non-so-official options and proper config files for the official stuff. Given how incomplete this logic is (i.e. the big variable for naming remains the kernel, which might expose sysfs attributes in newer versions that we check for and didn't exist in older versions — and other problems like this), I am simply not confident in giving this first-class exposure in a primary configuration file. Fixes: #10448
2018-12-10 19:10:19 +03:00
docs: document the new environment variables logind groks
2018-10-23 16:53:18 +03:00
* `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set overrides systemd-logind's
built-in EFI logic of requesting a reboot into the firmware. Takes a
boolean. If set to false the functionality is turned off entirely. If set to
true instead of requesting a reboot into the firmware setup UI through EFI a
file `/run/systemd/reboot-to-firmware-setup` is created whenever this is
requested. This file may be checked for by services run during system
shutdown in order to request the appropriate operation from the firmware in
an alternative fashion.
* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows
overriding of systemd-logind's built-in EFI logic of requesting a reboot into
the boot loader menu. Takes a boolean. If set to false the functionality is
turned off entirely. If set to true instead of requesting a reboot into the
boot loader menu through EFI a file `/run/systemd/reboot-to-boot-loader-menu`
is created whenever this is requested. The file contains the requested boot
loader menu timeout in µs, formatted in ASCII decimals, or zero in case no
time-out is requested. This file may be checked for by services run during
system shutdown in order to request the appropriate operation from the boot
loader in an alternative fashion.
* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows
overriding of systemd-logind's built-in EFI logic of requesting a reboot into
a specific boot loader entry. Takes a boolean. If set to false the
functionality is turned off entirely. If set to true instead of requesting a
reboot into a specific boot loader entry through EFI a file
`/run/systemd/reboot-to-boot-loader-entry` is created whenever this is
requested. The file contains the requested boot loader entry identifier. This
file may be checked for by services run during system shutdown in order to
request the appropriate operation from the boot loader in an alternative
fashion. Note that by default only boot loader entries which follow the [Boot
Loader Specification](https://systemd.io/BOOT_LOADER_SPECIFICATION) and are
placed in the ESP or the Extended Boot Loader partition may be selected this
way. However, if a directory `/run/boot-loader-entries/` exists, the entries
are loaded from there instead. The directory should contain the usual
directory hierarchy mandated by the Boot Loader Specification, i.e. the entry
drop-ins should be placed in
`/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by
the drop-ins (including the kernels and initrds) somewhere else below
`/run/boot-loader-entries/`. Note that all these files may be (and are
supposed to be) symlinks. systemd-logind will load these files on-demand,
these files can hence be updated (ideally atomically) whenever the boot
loader configuration changes. A foreign boot loader installer script should
hence synthesize drop-in snippets and symlinks for all boot entries at boot
or whenever they change if it wants to integrate with systemd-logind's APIs.
Rename $TEST_DIR to $SYSTEMD_TEST_DATA, document it TEST_DIR is rather generic, and we prefix all variables used by installed executables with "SYSTEMD_".
2017-02-15 03:17:38 +03:00
installed systemd tests:
* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
a test executable is moved to an arbitrary location.
documentation: document nss-systemd's internal environment variables in ENVIRONMENT.md
2017-09-20 19:28:29 +03:00
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`.
doc: add $SYSTEMD_TIMEDATED_NTP_SERVICES= in ENVIRONMENT.md (#8785)
2018-04-23 11:14:15 +03:00
systemd-timedated:
* `$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.
doc: document the two new env vars set by the service manager
2018-07-04 16:36:06 +03:00
sulogin-shell: Use force if SYSTEMD_SULOGIN_FORCE set When the root account is locked sulogin will either inform you of this and not allow you in or if --force is used it will hand you passwordless root (if using a recent enough version of util-linux). Not being allowed a shell is ofcourse inconvenient, but at the same time handing out passwordless root unconditionally is probably not a good idea everywhere. This patch thus allows to control which behaviour you want by setting the SYSTEMD_SULOGIN_FORCE environment variable to true or false to control the behaviour, eg. via adding this to 'systemctl edit rescue.service' (or emergency.service): [Service] Environment=SYSTEMD_SULOGIN_FORCE=1 Distributions who used locked root accounts and want the passwordless behaviour could thus simply drop in the override file in /etc/systemd/system/rescue.service.d/override.conf Fixes: #7115 Addresses: https://bugs.debian.org/802211
2018-10-14 15:53:09 +03:00
systemd-sulogin-shell:
* `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
root password is not available (such as when the root account is locked).
See `sulogin(8)` for more details.
efi: allow ESP validity checks to be turned off let's add an env var for this, as this really shouldn't be a top-level feature, as it turning off the validity checks certainly isn't advisable. Fixes: #4925
2018-06-25 16:08:24 +03:00
bootctl and other tools that access the EFI System Partition (ESP):
* `$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.
bootspec: introduce SYSTEMD_ESP_PATH for overriding where to look for the ESP (#10834)
2018-11-20 06:37:01 +03:00
* `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
may be used to override ESP path auto detection, and redirect any accesses to
the ESP to the specified directory. Not that unlike with bootctl's --path=
switch only very superficial validation of the specified path is done when
this environment variable is used.
doc: document the two new env vars set by the service manager
2018-07-04 16:36:06 +03:00
systemd itself:
* `$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.
remount-fs: optionally remount / writable, if we are told through an env var
2018-11-23 21:47:41 +03:00
systemd-remount-fs:
docs: fix typos and duplicate words s/and and/and/ s/explicity/explicitly/ s/that that/that/ s/the the/the/ s/is is/it is/ s/overriden/overridden/
2019-06-27 10:54:20 +03:00
* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and no entry for the root directory
remount-fs: optionally remount / writable, if we are told through an env var
2018-11-23 21:47:41 +03:00
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.
locale-util: suppress non-UTF-8 locales when enumerating them Let's hide non-UTF-8 locales by default. It's 2019 after all. Let's add an undocumented env var to reenable listing them though. This should substantially shorten the list of choices we offer users, and only show realistic choices. note that only firstboot and localectl make use of this information, and both allow configuration of values outside of these lists, hence all this change does is hide legacy options, but they are still available if you know what you do, and that's how it should be.
2019-07-12 14:38:43 +03:00
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.
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