systemd

Related articles
systemd/User
systemd/Timers
systemd/Journal
systemd/Sandboxing
systemd/FAQ
init
udev
Improving performance/Boot process
Allow users to shutdown
From the
project web page
:
systemd
is a suite of basic building blocks for a Linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.
systemd
provides aggressive parallelization capabilities, uses socket and
D-Bus
activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux
control groups
, maintains mount and automount points, and implements an elaborate transactional dependency-based service control logic. Other parts include a logging daemon, utilities to control basic system configuration like the hostname, date, locale, maintain a list of logged-in users and running containers and virtual machines, system accounts, runtime directories and settings, and daemons to manage simple network configuration, network time synchronization, log forwarding, and name resolution.
Historically, what systemd calls "service" was named
daemon
: any program that runs as a "background" process (without a terminal or user interface), commonly waiting for events to occur and offering services. A good example is a web server that waits for a request to deliver a page, or an ssh server waiting for someone trying to log in. While these are full featured applications, there are daemons whose work is not that visible. Daemons are for tasks like writing messages into a log file (e.g.
syslog
,
metalog
) or keeping your system time accurate (e.g.
ntpd
). For more information see
daemon(7)
.
Note
For a detailed explanation of why Arch moved to
systemd
, see
this forum post
.
Basic systemctl usage
The main command used to introspect and control
systemd
is
systemctl
. Some of its uses are examining the system state and managing the system and services. See
systemctl(1)
for more details.
Tip
You can use all of the following
systemctl
commands with the
-H
user
@
host
switch to control a
systemd
instance on a remote machine. This will use
SSH
to connect to the remote
systemd
instance.
Plasma
users can install
systemdgenie
as a graphical frontend for
systemctl
.
Using units
Units commonly include, but are not limited to, services (
.service
), mount points (
.mount
), devices (
.device
) and sockets (
.socket
).
When using
systemctl
, you generally have to specify the complete name of the unit file, including its suffix, for example
sshd.socket
. There are however a few short forms when specifying the unit in the following
systemctl
commands:
If you do not specify the suffix, systemctl will assume
.service
. For example,
netctl
and
netctl.service
are equivalent.
Mount points will automatically be translated into the appropriate
.mount
unit. For example, specifying
/home
is equivalent to
home.mount
.
Similar to mount points, devices are automatically translated into the appropriate
.device
unit, therefore specifying
/dev/sda2
is equivalent to
dev-sda2.device
.
See
systemd.unit(5)
for details.
Note
Some unit names contain an
@
sign (e.g.
name@
string
.service
): this means that they are
instances
of a
template
unit, whose actual file name does not contain the
string
part (e.g.
name@.service
).
string
is called the
instance identifier
, and is similar to an argument that is passed to the template unit when called with the
systemctl
command: in the unit file it will substitute the
%i
specifier. To be more accurate,
before
trying to instantiate the
name@.
suffix
template unit,
systemd
will actually look for a unit with the exact
name@
string
.
suffix
file name, although by convention such a "clash" happens rarely, i.e. most unit files containing an
@
sign are meant to be templates. Also, if a template unit is called without an instance identifier, it will generally fail (except with certain
systemctl
commands, like
cat
).
The commands in the below table operate on
system units
since
--system
is the implied default for
systemctl
. To instead operate on
user units
(for the
calling user
), use
systemctl --user
without root privileges. See also
systemd/User#Basic setup
to enable/disable user units for
all users
.
Tip
Most commands also work if multiple units are specified, see
systemctl(1)
for more information.
The
--now
switch can be used in conjunction with
enable
,
disable
, and
mask
to start or stop the unit
immediately
rather than after rebooting.
A package may offer units for different purposes. If you just installed a package,
pacman -Qql
package
| grep -Fe .service -e .socket
can be used to check and find them.
When available, enabling
unit
.socket
instead of
unit
.service
might be beneficial because the socket would start the service when necessary. See
#Socket activation
for more details.
Action
Command
Note
Analyzing the system state
Show system status
systemctl status
List running
units
systemctl
or
systemctl list-units
List failed
units
systemctl --failed
List installed
unit files
1
systemctl list-unit-files
Show process status
for a PID
systemctl status
pid
cgroup slice
, memory and parent
Checking the unit status
Show a manual page
associated with a unit
systemctl help
unit
as supported by the unit
Status
of a unit
systemctl status
unit
including whether it is running or not
Check
whether a unit is enabled
systemctl is-enabled
unit
Starting, restarting, reloading a unit
Start
a unit immediately
systemctl start
unit
as root
Stop
a unit immediately
systemctl stop
unit
as root
Restart
a unit
systemctl restart
unit
as root
Reload
a unit and its configuration
systemctl reload
unit
as root
Reload systemd manager
configuration
2
systemctl daemon-reload
as root
scan for new or changed units
Enabling a unit
Enable
a unit to start automatically at boot
systemctl enable
unit
as root
Enable
a unit to start automatically at boot and
start
it immediately
systemctl enable --now
unit
as root
Disable
a unit to no longer start at boot
systemctl disable
unit
as root
Disable
a unit to no longer start at boot and
stop
it immediately
systemctl disable --now
unit
as root
Reenable
a unit
3
systemctl reenable
unit
as root
i.e. disable and enable anew
Masking a unit
Mask
a unit to make it impossible to start
4
systemctl mask
unit
as root
Unmask
a unit
systemctl unmask
unit
as root
See
systemd.unit(5) § UNIT FILE LOAD PATH
for the directories where available unit files can be found.
This does not ask the changed units to reload their own configurations (see the
Reload
action).
For example, in case its
[Install]
section has changed since last enabling it.
Both manually and as a dependency, which makes masking dangerous. Check for existing masked units with:
$ systemctl list-unit-files --state=masked
Power management
polkit
is necessary for power management as an unprivileged user. If you are in a local
systemd-logind
user session and no other session is active, the following commands will work without root privileges. If not (for example, because another user is logged into a tty),
systemd
will automatically ask you for the root password.
Action
Command
Shut down and reboot the system
systemctl reboot
Shut down and power-off the system
systemctl poweroff
Suspend the system
systemctl suspend
Put the system into hibernation (write RAM to disk)
systemctl hibernate
Put the system into hybrid-sleep state (also called suspend-to-both, it saves RAM to disk and then suspends)
systemctl hybrid-sleep
First suspend the system, then wake up after a configured time in order to just hibernate the system
systemctl suspend-then-hibernate
Perform a reboot of the userspace-only with a
#Soft reboot
.
systemctl soft-reboot
Soft reboot
Soft reboot is a special kind of a userspace-only reboot operation that does not involve the kernel. It is implemented by
systemd-soft-reboot.service(8)
and can be invoked through
systemctl soft-reboot
. As with
kexec
, it skips firmware re-initialization, but additionally the system does not go through kernel initialization and
initramfs
, and unlocked
dm-crypt
devices remain attached.
When
/run/nextroot/
contains a valid root file system hierarchy (e.g. is the root mount of another distribution or another snapshot),
soft-reboot
would switch the system root into it, allowing for switching to another installation without losing states managed by kernel, e.g.
networking
.
Tip
/run/nextroot/
is not necessarily a mount point or backed by physical device. For example, it can reside in the
/run/
tmpfs.
systemd
will turn
/run/nextroot/
automatically into a mount point on
soft-reboot
.
Note
Do not invoke
systemctl soft-reboot
after package updates that involved the kernel and initramfs.
Writing unit files
The syntax of
systemd'
s unit files (
systemd.unit(5)
) is inspired by
XDG Desktop Entry Specification .desktop files
, which are in turn inspired by
Microsoft Windows .ini files
. Unit files are loaded from multiple locations (to see the full list, run
systemctl show --property=UnitPath
), but the main ones are (listed from lowest to highest precedence):
/usr/lib/systemd/system/
: units provided by installed packages
/run/systemd/system/
: units installed by the system administrator, deleted on power-off (useful for
#Editing provided units
)
/etc/systemd/system/
: units installed by the system administrator
Note
The load paths are completely different when running
systemd
in
user mode
.
systemd
unit names may only contain ASCII alphanumeric characters, underscores and periods. All other characters must be replaced by C-style "\x2d" escapes, or employ their predefined semantics ('@', '-'). See
systemd.unit(5)
and
systemd-escape(1)
for more information.
Look at the units installed by your packages for examples, as well as
systemd.service(5) § EXAMPLES
.
Tip
Comments prepended with
#
may be used in unit-files as well, but only in new lines. Do not use end-line comments after
systemd
parameters or the unit will fail to activate.
systemd-analyze(1)
can help verifying the work. See the
systemd-analyze verify FILE...
section of that page.
Handling dependencies
With
systemd
, dependencies can be resolved by designing the unit files correctly. The most typical case is when unit
A
requires unit
B
to be running before
A
is started. In that case add
Requires=
B
and
After=
B
to the
[Unit]
section of
A
. If the dependency is optional, add
Wants=
B
and
After=
B
instead. Note that
Wants=
and
Requires=
do not imply
After=
, meaning that if
After=
is not specified, the two units will be started in parallel.
Dependencies are typically placed on services and not on
#Targets
. For example,
network.target
is pulled in by whatever service configures your network interfaces, therefore ordering your custom unit after it is sufficient since
network.target
is started anyway.
Service types
There are several different start-up types to consider when writing a custom service file. This is set with the
Type=
parameter in the
[Service]
section:
Type=simple
(default):
systemd
considers the service to be started up immediately. The process must not fork. Do not use this type if other services need to be ordered on this service, unless it is socket activated.
Type=forking
:
systemd
considers the service started up once the process forks and the parent has exited. For classic daemons, use this type unless you know that it is not necessary. You should specify
PIDFile=
as well so
systemd
can keep track of the main process.
Type=oneshot
: this is useful for scripts that do a single job and then exit. You may want to set
RemainAfterExit=yes
as well so that
systemd
still considers the service as active after the process has exited. Setting
RemainAfterExit=yes
is appropriate for the units which change the system state (e.g., mount some partition). See also
[1]
for the differences of simple and oneshot.
Type=notify
: identical to
Type=simple
, but with the stipulation that the daemon will send a signal to
systemd
when it is ready. The reference implementation for this notification is provided by
libsystemd-daemon.so
.
Type=dbus
: the service is considered ready when the specified
BusName
appears on DBus's system bus.
Type=idle
:
systemd
will delay execution of the service binary until all jobs are dispatched unless these take longer than 5s, where the service binary is started anyway. Other than that its behaviour is very similar to
Type=simple
. It should never be used for service ordering and is intended for helping with console output readability.
See the
systemd.service(5) § OPTIONS
man page for a more detailed explanation of the
Type
values.
Editing provided units
This article or section needs expansion.
Reason:
We should fit "If
--runtime
is specified, the changes will be made temporarily in
/run/
and they will be lost on the next reboot." in here. An example would be passing debug flags to a service and not wanting to keep the changes permanently. (Discuss in
Talk:Systemd
)
To avoid conflicts with pacman, unit files provided by packages should not be directly edited. There are two safe ways to modify a unit without touching the original file: create a new unit file which
overrides the original unit
or create
drop-in snippets
which are applied on top of the original unit. For both methods, you must reload the unit afterwards to apply your changes. This can be done either by editing the unit with
systemctl edit
(which reloads the unit automatically) or by reloading all units with:
# systemctl daemon-reload
Tip
You can use
systemd-delta
to see which unit files have been overridden or extended and what exactly has been changed.
Use
systemctl cat
unit
to view the content of a unit file and all associated drop-in snippets.
Replacement unit files
Note
The replacement units will keep on being used even if Pacman updates the original units in the future. This method makes system maintenance more difficult and therefore the next approach is preferred.
To replace the unit file
/usr/lib/systemd/system/
unit
, create the file
/etc/systemd/system/
unit
and
reenable
the unit to update the symlinks.
Alternatively, run:
# systemctl edit --full
unit
This opens
/etc/systemd/system/
unit
in your editor (copying the installed version if it does not exist yet) and automatically reloads it when you finish editing.
Drop-in files
To create drop-in files for the unit file
/usr/lib/systemd/system/
unit
, create the directory
/etc/systemd/system/
unit
.d/
and place
.conf
files there to override or add new options.
systemd
will parse and apply these files on top of the original unit.
The easiest way to do this is to run:
# systemctl edit
unit
--drop-in=
drop_in_name
This opens the file
/etc/systemd/system/
unit
.d/
drop_in_name
.conf
in your text editor (creating it if necessary) and automatically reloads the unit when you are done editing.
Omitting the
--drop-in=
option will result in systemd using the default file name
override.conf
.
Note
The key must be still placed in the appropriate section in the override file.
Not all keys can be overridden with drop-in files. For example, for changing
Conflicts=
a replacement file
is necessary
.
You can use top-level drop-in files to affect all units of the same type. For example, a drop-in file in
/etc/systemd/system/service.d/
affects all
.service
units. You can see an example in
#Notifying about failed services
Revert to vendor version
To revert any changes to a unit made using
systemctl edit
do:
# systemctl revert
unit
Examples
For example, if you simply want to add an additional dependency to a unit, you may create the following file:
/etc/systemd/system/
unit
.d/customdependency.conf
[Unit]
Requires=
new dependency
After=
new dependency
As another example, in order to replace the
ExecStart
directive, create the following file:
/etc/systemd/system/
unit
.d/customexec.conf
[Service]
ExecStart=
ExecStart=
new command
Note how
ExecStart
must be cleared before being re-assigned
[2]
. The same holds for every item that can be specified multiple times, e.g.
OnCalendar
for timers.
One more example to automatically restart a service:
/etc/systemd/system/
unit
.d/restart.conf
[Service]
Restart=always
RestartSec=30
Service logging levels
For services that send logs directly to journald or syslog, you can control their verbosity by setting a numeric value between 0 and 6 for the
LogLevelMax=
parameter in the
[Service]
section using the methods described above. For example:
/etc/systemd/system/
unit
.d/override.conf
[Service]
LogLevelMax=3
The standard log levels are identical to those used to filter the
journal
. Setting a lower number excludes all higher and less important log messages from your journal.
Suppressing a service's standard output
If a service is echoing stdout and/or stderr output, by default this will end up in the journal as well. This behavior can be suppressed by setting
StandardOutput=null
and/or
StandardError=null
in the
[Service]
section. Other values than
null
can be used to further tweak this behavior. See
systemd.exec(5) § LOGGING_AND_STANDARD_INPUT/OUTPUT
.
Targets
systemd
uses
targets
to group units together via dependencies and as standardized synchronization points. They serve a similar purpose as
runlevels
but act a little differently. Each
target
is named instead of numbered and is intended to serve a specific purpose with the possibility of having multiple ones active at the same time. Some
target
s are implemented by inheriting all of the services of another
target
and adding additional services to it. There are
systemd
target
s that mimic the common SystemVinit runlevels.
Get current targets
The following should be used under
systemd
instead of running
runlevel
:
$ systemctl list-units --type=target
Create custom target
The runlevels that held a defined meaning under sysvinit (i.e., 0, 1, 3, 5, and 6); have a 1:1 mapping with a specific
systemd
target
. Unfortunately, there is no good way to do the same for the user-defined runlevels like 2 and 4. If you make use of those it is suggested that you make a new named
systemd
target
as
/etc/systemd/system/
your target
that takes one of the existing runlevels as a base (you can look at
/usr/lib/systemd/system/graphical.target
as an example), make a directory
/etc/systemd/system/
your target
.wants
, and then symlink the additional services from
/usr/lib/systemd/system/
that you wish to enable.
Mapping between SysV runlevels and systemd targets
SysV Runlevel
systemd Target
Notes
0
poweroff.target
Halt the system.
1, s, single
rescue.target
Single user mode.
2, 4
multi-user.target
User-defined/Site-specific runlevels. By default, identical to 3.
3
multi-user.target
Multi-user, non-graphical. Users can usually login via multiple consoles or via the network.
5
graphical.target
Multi-user, graphical. Usually has all the services of runlevel 3 plus a graphical login.
6
reboot.target
Reboot
emergency
emergency.target
Emergency shell
Change current target
In
systemd
, targets are exposed via
target units
. You can change them like this:
# systemctl isolate graphical.target
This will only change the current target, and has no effect on the next boot. This is equivalent to commands such as
telinit 3
or
telinit 5
in Sysvinit.
Change default target to boot into
The standard target is
default.target
, which is a symlink to
graphical.target
. This roughly corresponds to the old runlevel 5.
To verify the current target with
systemctl
:
$ systemctl get-default
To change the default target to boot into, change the
default.target
symlink. With
systemctl
:
# systemctl set-default multi-user.target
Removed /etc/systemd/system/default.target.
Created symlink /etc/systemd/system/default.target -> /usr/lib/systemd/system/multi-user.target.
Alternatively, append one of the following
kernel parameters
to your boot loader:
systemd.unit=multi-user.target
(which roughly corresponds to the old runlevel 3),
systemd.unit=rescue.target
(which roughly corresponds to the old runlevel 1).
Default target order
systemd
chooses the
default.target
according to the following order:
Kernel parameter shown above
Symlink of
/etc/systemd/system/default.target
Symlink of
/usr/lib/systemd/system/default.target
systemd components
Some (not exhaustive) components of
systemd
are:
kernel-install
— to automatically move
kernels
and their respective
initramfs
images to the boot partition;
systemd-analyze(1)
— may be used to determine boot-up performance,  statistics and retrieve other state and tracing information, and to verify the correctness of unit files. It is also used to access special functions useful for advanced debugging.
systemd-boot
— simple UEFI
boot manager
;
systemd-creds
— to securely store and retrieve credentials used by systemd units;
systemd-cryptenroll
— Enroll PKCS#11, FIDO2, TPM2 token/devices to LUKS2 encrypted volumes;
systemd-firstboot
— basic system setting initialization before first boot;
systemd-homed
— portable human-user
accounts
;
systemd-logind(8)
—
session management
;
systemd-networkd
—
network configuration
management;
systemd-nspawn
— light-weight namespace container;
systemd-repart
— creates partition tables, adds or grows partitions;
systemd-resolved
— network
name resolution
;
systemd-run(1)
/
run0
— Temporarily and interactively acquire elevated or different privileges.
systemd-stub(7)
— a UEFI boot stub used for creating
unified kernel images
;
systemd-sysusers(8)
— creates system users and groups and adds users to groups at package installation or boot time;
systemd-timesyncd
—
system time
synchronization across the network;
systemd/Journal
— system logging;
systemd/Timers
— monotonic or realtime timers for controlling
.service
files or events, reasonable alternative to
cron
.
systemd.mount - mounting
systemd
is in charge of mounting the partitions and filesystems specified in
/etc/fstab
. The
systemd-fstab-generator(8)
translates all the entries in
/etc/fstab
into
systemd
units; this is performed at boot time and whenever the configuration of the system manager is reloaded.
systemd
extends the usual
fstab
capabilities and offers additional mount options. These affect the dependencies of the mount unit. They can, for example, ensure that a mount is performed only once the network is up or only once another partition is mounted. The full list of specific
systemd
mount options, typically prefixed with
x-systemd.
, is detailed in
systemd.mount(5) § FSTAB
.
An example of these mount options is
automounting
, which means mounting only when the resource is required rather than automatically at boot time. This is provided in
fstab#Automount with systemd
.
GPT partition automounting
On UEFI-booted systems, GPT partitions such as
root
,
home
,
swap
, etc. can be mounted automatically following the
Discoverable Partitions Specification
. These partitions can thus be omitted from
fstab
, and if the root partition is automounted, then
root=
can be omitted from the kernel command line. See
systemd-gpt-auto-generator(8)
.
The prerequisites are:
When using
mkinitcpio
, the
systemd hook
is required to automount the
root
partition.
All automounted partitions must reside on the same physical disk as the ESP.
The correct GPT partition types must be set. See
Partitioning#Partition scheme
.
The boot loader must set the
LoaderDevicePartUUID
EFI variable, so that the used EFI system partition can be identified. This is supported by
systemd-boot
,
systemd-stub(7)
,
Limine
,
GRUB
(with
grub-mkconfig
generated
grub.cfg
; custom
grub.cfg
requires
loading the bli module
) and
rEFInd (not enabled by default)
. This can be verified by running
bootctl
and checking if there is a line with
Partition:
under
Current Boot Loader
or
Current Stub
when booting via
Unified kernel images
.
udev
will create
symlinks to the discovered partitions
which can be used to reference the partitions and volumes in configuration files.
Tip
The automounting of a partition can be disabled by changing the partition's
type GUID
or setting the partition attribute bit 63 "do not automount", see
gdisk#Prevent GPT partition automounting
.
/var
For
/var
automounting to work, the PARTUUID must match the SHA256 HMAC hash of the partition type UUID keyed by the machine ID. The required PARTUUID can be obtained using:
$ systemd-id128 -u var-partition-uuid
Note
systemd-id128(1)
reads the machine ID from
/etc/machine-id
, this makes it impossible to know the needed PARTUUID before the system is installed.
systemd-sysvcompat
The primary role of
systemd-sysvcompat
(required by
base
) is to provide the traditional linux
init
binary. For
systemd
-controlled systems,
init
is just a symbolic link to its
systemd
executable.
In addition, it provides four convenience shortcuts that
SysVinit
users might be used to. The convenience shortcuts are
halt(8)
,
poweroff(8)
,
reboot(8)
and
shutdown(8)
. Each one of those four commands is a symbolic link to
systemctl
, and is governed by
systemd
behavior. Therefore, the discussion at
#Power management
applies.
systemd
-based systems can give up those System V compatibility methods by using the
init=
boot parameter
(see, for example,
/bin/init is in systemd-sysvcompat ?
) and
systemd
native
systemctl
command arguments.
systemd-tmpfiles - temporary files
systemd-tmpfiles
creates, deletes and cleans up volatile and temporary files and directories. It reads configuration files in
/etc/tmpfiles.d/
and
/usr/lib/tmpfiles.d/
to discover which actions to perform. Configuration files in the former directory take precedence over those in the latter directory.
Configuration files are usually provided together with service files, and they are named in the style of
/usr/lib/tmpfiles.d/
program
.conf
. For example, the
Samba
daemon expects the directory
/run/samba
to exist and to have the correct permissions. Therefore, the
samba
package ships with this configuration:
/usr/lib/tmpfiles.d/samba.conf
D /run/samba 0755 root root
Configuration files may also be used to write values into certain files on boot. For example, if you used
/etc/rc.local
to disable wakeup from USB devices with
echo USBE > /proc/acpi/wakeup
, you may use the following tmpfile instead:
/etc/tmpfiles.d/disable-usb-wake.conf
#    Path                  Mode UID  GID  Age Argument
w!   /proc/acpi/wakeup     -    -    -    -   USBE
An exclamation mark
!
signifies that the line is only applied at boot. This will prevent re-enabling the wakeup trigger if systemd-tmpfiles is run again after boot (for example by the pacman hook).
It is possible to write multiple lines to the same file, either with
\n
in the argument or using the
w+
type on multiple lines (including the first one) for
appending
:
/etc/tmpfiles.d/disable-usb-wake.conf
#    Path                  Mode UID  GID  Age Argument
w+!  /proc/acpi/wakeup     -    -    -    -   USBE
w+!  /proc/acpi/wakeup     -    -    -    -   LID0
See the
systemd-tmpfiles(8)
and
tmpfiles.d(5)
man pages for details.
Note
This method may not work to set options in
/sys
since the
systemd-tmpfiles-setup
service may run before the appropriate device modules are loaded. In this case, you could check whether the module has a parameter for the option you want to set with
modinfo
module
and set this option with a
config file in /etc/modprobe.d
. Otherwise, you will have to write a
udev rule
to set the appropriate attribute as soon as the device appears.
Drop-in configuration files
The factual accuracy of this article or section is disputed.
Reason:
This page is about PID 1 (init), and unit drop-ins are already mentioned. Drop-in is a generic concept, plus other systemd components have their dedicated wiki pages. Therefore this section doesn't seem to belong here. (Discuss in
Talk:Systemd#YHNdnzj : Configuration files in conf.d / drop-in snippets: misplaced?
)
Configuration files provided by packages should not be directly edited to avoid conflicts with pacman updates. For this, many (but not all) systemd packages provide a way to modify the configuration, but without touching the original file by creation of drop-in snippets. Check the package manual to see if drop-in configuration files are supported.
To create a drop-in configuration file for the unit file
/etc/systemd/
unit
.conf
, create the directory
/etc/systemd/
unit
.conf.d/
and place
.conf
files there to override or add new options.
systemd
will parse and apply these files on top of the original unit.
Check the overall configuration:
$ systemd-analyze cat-config systemd/
unit
.conf
The applied drop-in snippets file(s) and content will be listed at the end.
Restart
the service for the changes to take effect.
Tips and tricks
Socket activation
Some packages provide a
.socket
unit. For example,
cups
provides a
cups.socket
unit
[3]
. If
cups.socket
is
enabled
(and
cups.service
is left disabled),
systemd
will not start CUPS immediately; it will just listen to the appropriate sockets. Then, whenever a program attempts to connect to one of these CUPS sockets,
systemd
will start
cups.service
and transparently hand over control of these ports to the CUPS process.
GUI configuration tools
systemadm
— Graphical browser for
systemd
units. It can show the list of units, possibly filtered by type.
https://github.com/systemd/systemd-ui
||
systemd-ui
systemdGenie
—
systemd
management utility based on KDE technologies.
https://apps.kde.org/systemdgenie/
||
systemdgenie
isd
—  TUI for working with
systemd
units.
https://github.com/kainctl/isd
||
isd
Running services after the network is up
To delay a service until after the network is up, include the following dependencies in the
.service
file:
/etc/systemd/system/
foo
.service
[Unit]
...
Wants=network-online.target
After=network-online.target
...
The network wait service of the
network manager
in use must also be enabled so that
network-online.target
properly reflects the network status.
If using
NetworkManager
,
NetworkManager-wait-online.service
should be enabled together with
NetworkManager.service
. Check if this is the case with
systemctl is-enabled NetworkManager-wait-online.service
. If it is not enabled, then
reenable
NetworkManager.service
.
In the case of
netctl
,
enable
the
netctl-wait-online.service
(unless you are using
netctl-auto
; see
FS#75836
).
If using
systemd-networkd
,
systemd-networkd-wait-online.service
should be enabled together with
systemd-networkd.service
. Check if this is the case with
systemctl is-enabled systemd-networkd-wait-online.service
. If it is not enabled, then
reenable
systemd-networkd.service
.
For more detailed explanations, see the discussion in the
Network configuration synchronization points
.
If a service needs to perform DNS queries, it should additionally be ordered after
nss-lookup.target
:
/etc/systemd/system/
foo
.service
[Unit]
...
Wants=network-online.target
After=network-online.target nss-lookup.target
...
See
systemd.special(7) § Special Passive System Units
.
For
nss-lookup.target
to have any effect it needs a service that pulls it in via
Wants=nss-lookup.target
and orders itself before it with
Before=nss-lookup.target
. Typically this is done by local
DNS resolvers
.
Check which active service, if any, is pulling in
nss-lookup.target
with:
$ systemctl list-dependencies --reverse nss-lookup.target
Enable installed units by default
This article or section needs expansion.
Reason:
How does it work with instantiated units? (Discuss in
Talk:Systemd
)
By default, Arch Linux does not make use of systemd presets, and does not enable most services on installation.
If you wish for systemd presets to be honored when packages are installed, you will need to create a
a pacman hook
in order to run
systemctl preset
or
systemctl preset-all
whenever a new systemd unit is installed. Something like
/etc/pacman.d/hooks/40-systemd-presets.hook
[Trigger]
Operation = Install
Type = Path
Target = usr/lib/systemd/system/*.service
Target = usr/lib/systemd/system/*.timer
Target = usr/lib/systemd/system/*.socket
Target = usr/lib/systemd/system/*.slice
Target = usr/lib/systemd/system/*.path
Target = usr/lib/systemd/system/*.target

[Action]
Description = Run systemctl preset
When = PostTransaction
Depends = systemd
NeedsTargets
# Alternatively, you could just run systemd preset-all.
# However, note that this will reset ALL services to the defaults,
# which is probably not what you want unless you have carefully configured
# your presets.
Exec = /etc/pacman.d/scripts/systemd-presets-hook
/etc/pacman.d/scripts/systemd-presets-hook
#!/bin/sh -e

while read -r f; do
    unit="${f##*/}"
    # alternatively, you could read all the units and pass them to systemctl preset in a single invocation
    systemctl preset "$unit"
done
Arch Linux ships with
/usr/lib/systemd/system-preset/99-default.preset
containing
disable *
. This causes
systemctl preset
to disable all units by default, such that when a new package is installed, the user must manually enable the unit.
To enable units by default instead, simply create a symlink from
/etc/systemd/system-preset/99-default.preset
to
/dev/null
or replace with a file containing
enable *
in order to override the configuration file. This will cause
systemctl preset
to enable all units that get installed—regardless of unit type—unless specified in another file in one
systemctl preset'
s configuration directories. User units are not affected. It is also possible to configure higher priority files with more specific rules on what should be enabled. See
systemd.preset(5)
for more information.
Note
Enabling all units by default may cause problems with packages that contain two or more mutually exclusive units.
systemctl preset
is designed to be used by distributions and spins or system administrators. In the case where two conflicting units would be enabled, you should explicitly specify which one is to be disabled in a preset configuration file as specified in the
systemd.preset(5)
man page.
Sandboxing application environments
See
systemd/Sandboxing
.
Notifying about failed services
In order to notify about service failures, an
OnFailure=
directive needs to be added to the according service file, for example by using a
drop-in configuration file
. Adding this directive to every service unit can be achieved with a top-level drop-in configuration file. For details about top-level drop-ins, see
systemd.unit(5)
.
Create a top-level drop-in for services:
/etc/systemd/system/service.d/toplevel-override.conf
[Unit]
OnFailure=failure-notification@%n.service
This adds
OnFailure=failure-notification@%n.service
to every service file. If
some_service_unit
fails,
failure-notification@
some_service_unit
.service
will be started to handle the notification delivery (or whatever task it is configured to perform).
Create the
failure-notification@.service
template unit:
/etc/systemd/system/failure-notification@.service
[Unit]
Description=Send a notification about a failed systemd unit

[Service]
Type=oneshot
ExecStart=/
path
/
to
/failure-notification.sh %i
# runs as a temporary user/group and enables several other security precautions
DynamicUser=true
You can create the
failure-notification.sh
script and define what to do or how to notify. Examples include
sending e-mail
,
showing desktop notifications
, using gotify, XMPP, etc. The
%i
will be the name of the failed service unit and will be passed as an argument to the script.
In order to prevent a recursion for starting instances of
failure-notification@.service
again and again if the start fails, create an empty drop-in configuration file with the same name as the top-level drop-in (the empty service-level drop-in configuration file takes precedence over the top-level drop-in and overrides the latter one):
# mkdir /etc/systemd/system/failure-notification@.service.d
# touch /etc/systemd/system/failure-notification@.service.d/toplevel-override.conf
Notifying with e-mail
You can set up systemd to send an e-mail when a unit fails. Cron sends mail to
MAILTO
if the job outputs to stdout or stderr, but many jobs are setup to only output on error. First you need two files: an executable for sending the mail and a
.service
for starting the executable. For this example, the executable is just a shell script using
sendmail
, which is in packages that provide
smtp-forwarder
.
/usr/local/bin/systemd-email
#!/bin/sh

/usr/bin/sendmail -t <<ERRMAIL
To: $1
From: systemd <root@$HOSTNAME>
Subject: $2
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset=UTF-8

$(systemctl status --full "$2")
ERRMAIL
Whatever executable you use, it should probably take at least two arguments as this shell script does: the address to send to and the unit file to get the status of. The
.service
we create will pass these arguments:
/etc/systemd/system/status_email_
user
@.service
[Unit]
Description=status email for %i to
user
[Service]
Type=oneshot
ExecStart=/usr/local/bin/systemd-email
address
%i
User=nobody
Group=systemd-journal
Where
user
is the user being emailed and
address
is that user's email address. Although the recipient is hard-coded, the unit file to report on is passed as an instance parameter, so this one service can send email for many other units. At this point you can
start
status_email_
user
@dbus.service
to verify that you can receive the emails.
Then simply
edit
the service you want emails for and add
OnFailure=status_email_
user
@%n.service
to the
[Unit]
section.
%n
passes the unit's name to the template.
Note
If you set up sSMTP security according to
sSMTP#Security
the user
nobody
will not have access to
/etc/ssmtp/ssmtp.conf
, and the
systemctl start status_email_
user
@dbus.service
command will fail. One solution is to use
root
as the User in the
status_email_
user
@.service
unit.
If you try to use
mail -s somelogs
address
in your email script,
mail
will fork and systemd will kill the mail process when it sees your script exit. Make the mail non-forking by doing
mail -Ssendwait -s somelogs
address
.
Tip
Newer versions of systemd recommend using
DynamicUser=true
as a replacement for
User=nobody
which is now discouraged. See
GitHub issue 428
for more details.
Automatically turn off an external HDD at shutdown
See
udisks#Automatically turn off an external HDD at shutdown
.
Troubleshooting
Investigating failed services
To find the
systemd
services which failed to start:
$ systemctl --failed
To find out why they failed, examine their log output. See
systemd/Journal#Filtering output
for details.
Tip
It is possible to clear the "failed" status of units, removing them from the output of
systemctl --failed
:
# systemctl reset-failed
unit
Note that this usually unloads the unit (see
CollectMode
documentation within
systemd.unit(5)
), which notably makes
systemctl status
no longer report their failed status or logs.
Diagnosing boot problems
systemd
has several options for diagnosing problems with the boot process. See
boot debugging
for more general instructions and options to capture boot messages before
systemd
takes over the
boot process
. Also see
systemd debugging documentation
.
Diagnosing a systemd-provided service
If some service
provided by systemd itself
misbehaves, or you want to get more information about what it is doing, set the
SYSTEMD_LOG_LEVEL
environment variable
to
debug
.
For example, to run the
systemd-networkd
daemon in debug mode,
edit the service temporarily
using
systemctl edit --runtime
and add the two lines:
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug
Then, start watching the journal for the service with
journalctl(1)
's
-f
/
--follow
option, and
restart
systemd-networkd
.
Note
Some "core" services, such as
systemd-logind
, cannot be restarted without breaking e.g. screen and/or session management.
Shutdown/reboot takes terribly long
If the shutdown process takes a very long time (or seems to freeze), most likely a service not exiting is to blame.
systemd
waits some time for each service to exit before trying to kill it. To find out whether you are affected, see
Shutdown completes eventually
in the
systemd
documentation.
A common problem is a stalled shutdown or suspend process. To verify whether that is the case, you could run either of these commands and check the outputs
# systemctl poweroff
Failed to power off system via logind: There's already a shutdown or sleep operation in progress
# systemctl list-jobs
JOB UNIT                    TYPE  STATE
...
21593 systemd-suspend.service start running
21592 suspend.target          start waiting
..
The
solution
to this would be to cancel these jobs by running
# systemctl cancel
# systemctl stop systemd-suspend.service
and then trying shutdown or reboot again.
Short lived processes do not seem to log any output
If running
journalctl -u foounit
as root does not show any output for a short lived service, look at the PID instead. For example, if
systemd-modules-load.service
fails, and
systemctl status systemd-modules-load
shows that it ran as PID 123, then you might be able to see output in the journal for that PID, i.e. by running
journalctl -b _PID=123
as root. Metadata fields for the journal such as
_SYSTEMD_UNIT
and
_COMM
are collected asynchronously and rely on the
/proc
directory for the process existing. Fixing this requires fixing the kernel to provide this data via a socket connection, similar to
SCM_CREDENTIALS
. In short, it is a
bug
. Keep in mind that immediately failed services might not print anything to the journal as per design of
systemd
.
Boot time increasing over time
The factual accuracy of this article or section is disputed.
Reason:
NetworkManager issues are not
systemd
's fault, the alleged reports are missing. Slow
systemctl status
or
journalctl
do not affect boot time. (Discuss in
Talk:Systemd
)
After using
systemd-analyze
a number of users have noticed that their boot time has increased significantly in comparison with what it used to be. After using
systemd-analyze blame
NetworkManager
is being reported as taking an unusually large amount of time to start.
The problem for some users has been due to
/var/log/journal
becoming too large. This may have other impacts on performance, such as for
systemctl status
or
journalctl
. As such the solution is to remove every file within the folder (ideally making a backup of it somewhere, at least temporarily) and then setting a journal file size limit as described in
systemd/Journal#Journal size limit
.
systemd-tmpfiles-setup.service fails to start at boot
Starting with
systemd
219,
/usr/lib/tmpfiles.d/systemd.conf
specifies ACL attributes for directories under
/var/log/journal
and, therefore, requires ACL support to be enabled for the filesystem the journal resides on.
See
Access Control Lists#Enable ACL
for instructions on how to enable ACL on the filesystem that houses
/var/log/journal
.
Disable emergency mode on remote machine
You may want to disable emergency mode on a remote machine, for example, a virtual machine hosted at Azure or Google Cloud. It is because if emergency mode is triggered, the machine will be blocked from connecting to network.
To disable it,
mask
emergency.service
and
emergency.target
.
Error "Unit xxx.service not found", but service does exist
You may be trying to start or enable a user unit as a system unit.
systemd.unit(5)
indicates, which units reside where. By default
systemctl
operates on system services.
See
systemd/User
for more details.
Manually renewing LoaderDevicePartUUID after changing EFI partition UUID
Some bootloaders only set the
LoaderDevicePartUUID
variable when it is empty. Consequently, even if the UUID of the EFI partition changes, the bootloader will not update
LoaderDevicePartUUID
. By deleting the EFI variable with the commands below, the bootloader will then repopulate it with the new UUID.
# chattr -i /sys/firmware/efi/efivars/LoaderDevicePartUUID-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
# rm /sys/firmware/efi/efivars/LoaderDevicePartUUID-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
See also
Wikipedia:systemd
Official web site
systemd optimizations
systemd FAQ
systemd Tips and tricks
systemd(1)
Other distributions
Gentoo:systemd
Fedora:systemd
Fedora:How to debug Systemd problems
Fedora:SysVinit to Systemd Cheatsheet
Debian:systemd
Lennart's blog story
,
update 1
,
update 2
,
update 3
,
summary
Debug Systemd Services
systemd for Administrators (PDF)
How To Use Systemctl to Manage Systemd Services and Units
Session management with systemd-logind
Emacs#Syntax highlighting for systemd files
Two
part
introductory article in
The H Open
magazine.