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. systemd supports SysV and LSB init scripts and works as a replacement for sysvinit. 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.
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. Seefor more details.
- You can use all of the following systemctl commands with the
-H user@hostswitch to control a systemd instance on a remote machine. This will use SSH to connect to the remote systemd instance.
- Plasma users can install AUR as a graphical frontend for systemctl. After installing the module will be added under System administration.
Units can be, for example, services (.service), mount points (.mount), devices (.device) or 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,
- Mount points will automatically be translated into the appropriate .mount unit. For example, specifying
/homeis equivalent to
- Similar to mount points, devices are automatically translated into the appropriate .device unit, therefore specifying
/dev/sda2is equivalent to
email@example.com): this means that they are instances of a template unit, whose actual file name does not contain the
stringis 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
%ispecifier. To be more accurate, before trying to instantiate the
name@.suffixtemplate unit, systemd will actually look for a unit with the exact
firstname.lastname@example.org 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 just fail, since the
%ispecifier cannot be substituted.
- Most of the following commands also work if multiple units are specified, see for more information.
--nowswitch can be used in conjunction with
maskto respectively start, stop, or mask 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 .socketcan be used to check and find them.
|Analyzing the system state|
|Show system status||
|List running units||
|List failed units||
|List installed unit files1||
|Show process status for a PID||
||cgroup slice, memory and parent|
|Checking the unit status|
|Show a manual page associated with a unit||
||as supported by the unit|
|Status of a unit||
||including whether it is running or not|
|Check whether a unit is enabled||
|Starting, restarting, reloading a unit|
|Start a unit immediately||
|Stop a unit immediately||
|Restart a unit||
|Reload a unit and its configuration||
|Reload systemd manager configuration2||
||scan for new or changed units|
|Enabling a unit|
|Enable a unit to start automatically at boot||
|Enable a unit to start automatically at boot and start it immediately||
|Disable a unit to no longer start at boot||
|Reenable a unit3||
||i.e. disable and enable anew|
|Masking a unit|
|Mask a unit to make it impossible to start4||
|Unmask a unit||
- See 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.
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.
|Shut down and reboot the system|
|Shut down and power-off the system|
|Suspend the system|
|Put the system into hibernation|
|Put the system into hybrid-sleep state (or suspend-to-both)|
Writing unit files
The syntax of systemd's unit files (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
/etc/systemd/system/: units installed by the system administrator
- 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 and for more information.
Look at the units installed by your packages for examples, as well as.
#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.
With systemd, dependencies can be resolved by designing the unit files correctly. The most typical case is that the unit A requires the unit B to be running before A is started. In that case add
After=B to the
[Unit] section of A. If the dependency is optional, add
After=B instead. Note that
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.
There are several different start-up types to consider when writing a custom service file. This is set with the
Type= parameter in the
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=yesas well so that systemd still considers the service as active after the process has exited.
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
BusNameappears on DBus's system bus.
Type=idle: systemd will delay execution of the service binary until all jobs are dispatched. Other than that behavior is very similar to
Editing provided units
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
- You can use systemd-delta to see which unit files have been overridden or extended and what exactly has been changed.
systemctl cat unitto view the content of a unit file and all associated drop-in snippets.
Replacement unit files
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.
# systemctl edit --full unit
/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.
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
This opens the file
/etc/systemd/system/unit.d/override.conf in your text editor (creating it if necessary) and automatically reloads the unit when you are done editing.
Conflicts=a replacement file is necessary.
Revert to vendor version
To revert any changes to a unit made using
systemctl edit do:
# systemctl revert unit
For example, if you simply want to add an additional dependency to a unit, you may create the following file:
[Unit] Requires=new dependency After=new dependency
As another example, in order to replace the
ExecStart directive for a unit that is not of type
oneshot, create the following file:
[Service] ExecStart= ExecStart=new command
ExecStart must be cleared before being re-assigned . 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:
[Service] Restart=always RestartSec=30
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 targets are implemented by inheriting all of the services of another target and adding additional services to it. There are systemd targets that mimic the common SystemVinit runlevels so you can still switch targets using the familiar
telinit RUNLEVEL command.
Get current targets
The following should be used under systemd instead of running
$ 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||runlevel0.target, poweroff.target||Halt the system.|
|1, s, single||runlevel1.target, rescue.target||Single user mode.|
|2, 4||runlevel2.target, runlevel4.target, multi-user.target||User-defined/Site-specific runlevels. By default, identical to 3.|
|3||runlevel3.target, multi-user.target||Multi-user, non-graphical. Users can usually login via multiple consoles or via the network.|
|5||runlevel5.target, graphical.target||Multi-user, graphical. Usually has all the services of runlevel 3 plus a graphical login.|
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 bootloader:
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
- Symlink of
Some (not exhaustive) components of systemd are:
- systemd-boot — simple UEFI boot manager;
- systemd-firstboot — basic system setting initialization before first boot;
- systemd-homed — portable human-user accounts;
- systemd-logind — session management;
- systemd-networkd — network configuration management;
- systemd-nspawn — light-weight namespace container;
- systemd-resolved — network name resolution;
- — 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 controling
.servicefiles or events, reasonable alternative to cron.
systemd.mount - mounting
systemd is in charge of mounting the partitions and filesystems specified in
/etc/fstab. The 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 .
An example of these mount options in the context of automounting, which means mounting only when the resource is required rather than automatically at boot time, is provided in fstab#Automount with systemd.
GPT partition automounting
/var/tmp 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 --app-specific=partition-type-UUID machine-id
partition-type-UUID with the appropriate partition type UUID value from the Discoverable Partitions Specification.
/etc/machine-id, this makes it impossible to know the needed PARTUUID before the system is installed.
init binary. For systemd controlled systems,
init is just a symbolic link to its
In addition, it also provides 4 convenience short cuts that SysVinit users might be used to. The convenience short cuts are , , and . Each one of those 4 commands is a symbolic link to
systemctl, and 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, [solved] /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
/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 package ships with this configuration:
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:
# Path Mode UID GID Age Argument w /proc/acpi/wakeup - - - - USBE
See theand man pages for details.
/syssince the systemd-tmpfiles-setup service may run before the appropriate device modules is loaded. In this case you could check whether the module has a parameter for the option you want to set with
modinfo moduleand 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.
Tips and tricks
GUI configuration tools
- systemadm — Graphical browser for systemd units. It can show the list of units, possibly filtered by type.
- SystemdGenie — systemd management utility based on KDE technologies.
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:
[Unit] ... Wants=network-online.target After=network-online.target ...
The network wait service of the particular application that manages the network, must also be enabled so that
network-online.target properly reflects the network status.
- If using NetworkManager,
NetworkManager-wait-online.serviceis 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
- In the case of netctl, enable the
- If using systemd-networkd,
systemd-networkd-wait-online.serviceis 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
For more detailed explanations see Running services after the network is up in the systemd wiki.
If a service needs to perform DNS queries, it should additionally be ordered after
[Unit] ... Wants=network-online.target After=network-online.target nss-lookup.target ...
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
$ systemctl list-dependencies --reverse nss-lookup.target
Enable installed units by default
Arch Linux ships with
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.
If this behavior is not desired, simply create a symlink from
/dev/null 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. See for more information.
Sandboxing application environments
A unit file can be created as a sandbox to isolate applications and their processes within a hardened virtual environment. systemd leverages namespaces, a list of allowed/denied capabilities, and control groups to container processes through an extensive execution environment configuration— .
The enhancement of an existing systemd unit file with application sandboxing typically requires trial-and-error tests accompanied by the generous use of stderr and error logging and output facilities. You may want to first search upstream documentation for already done tests to base trials on. To get a starting point for possible hardening options, run,
$ systemd-analyze security unit
Some examples of how sandboxing with systemd can be deployed:
CapabilityBoundingSetdefines a list of that are allowed or denied for a unit. See .
CAP_SYS_ADMcapability, for example, which should be one of the goals of a secure sandbox:
Notifying about failed services
In order to notify about service failures, a
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 .
Create a top-level drop-in for services:
OnFailure=failure-notification@%n to every service file. If some_service_unit fails,
failure-notification@some_service_unit will be started to handle the notification delivery (or whatever task it is configured to perform).
failure-notification@ template unit:
[Unit] Description=Send a notification about a failed systemd unit After=network.target [Service] Type=simple ExecStart=/path/to/failure-notification.sh %i
You can create the
failure-notification.sh script and define what to do or how to notify (mail, gotify, xmpp, etc.). The
%i will be the name of the failed service unit and will be passed as argument to the script.
In order to prevent a regression for instances of
failure-notification@.service, 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 -p /etc/systemd/system/failure-notification@.service.d # touch /etc/systemd/system/failure-notification@.service.d/toplevel-override.conf
Investigating failed services
To find the systemd services which failed to start:
$ systemctl --state=failed
To find out why they failed, examine their log output. See systemd/Journal#Filtering output for details.
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 the systemd debugging documentation.
Diagnosing a service
If some systemd service misbehaves or you want to get more information about what is happening, set the
SYSTEMD_LOG_LEVEL environment variable to
debug. For example, to run the systemd-networkd daemon in debug mode:
Add a drop-in file for the service adding the two lines:
Or equivalently, set the environment variable manually:
# SYSTEMD_LOG_LEVEL=debug /lib/systemd/systemd-networkd
then restart systemd-networkd and watch the journal for the service with the
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 if you are affected, see this article.
Short lived processes do not seem to log any output
journalctl -u foounit 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.
journalctl -b _PID=123. Metadata fields for the journal such as
_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
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
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
- Official web site
- Manual pages
- Other distributions
- 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.