systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. 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 cgroups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic. It can work as a drop-in replacement for sysvinit. For more information, watch the video at http://linuxconfau.blip.tv/file/4696791/ or http://www.youtube.com/watch?v=TyMLi8QF6sw
- 1 Why systemd?
- 2 systemd documentation
- 3 Tools
- 4 Boot Kernel Command Line
- 5 What is the tool to manage services with systemd?
- 6 How do I start/stop or enable/disable services?
- 7 How do I change the runlevel?
- 8 How do I change the default runlevel?
- 9 How do I know the current run level?
- 10 How to power off the machine ?
- 11 Does service command work with systemd?
- 12 Does chkconfig command work with systemd?
- 13 Does system-config-services work with systemd?
- 14 How do I change the number of gettys running by default?
- 15 How do I set automatic login on a virtual console terminal?
- 16 How do I customize a unit file/ add a custom unit file?
- 17 How do I debug systemd issues?
- 18 Readahead
- 19 Warnings on separate /usr partition
- 20 Man pages
- 21 References
systemd has very comprehensive documentation. Refer to
systemctl: used to introspect and control the state of the systemd system and service manager
systemd-cgls: recursively shows the contents of the selected Linux control group hierarchy in a tree
systemadm: a graphical frontend for the systemd system and service manager that allows introspection and control of systemd. Part of the systemd-gtk page. This is a early version and needs more work. Do not use it for now unless you are a developer.
View the man pages for more details.
Boot Kernel Command Line
On boot systemd activates (by default), the target unit default.target whose job is to activate services and other units by pulling them in via dependencies.
To override the unit to activate, systemd parses its own kernel command line arguments via the
systemd.unit= command line option. This may be used to temporarily boot into a different boot unit. The classical run-levels are replaced as following:
systemd.unit=rescue.target is a special target unit for setting up the base system and a rescue shell (similar to run level 1);
systemd.unit=emergency.target, is very similar to passing
init=/bin/sh but with the option to boot the full system from there;
systemd.unit=multi-user.target for setting up a non-graphical multi-user system;
systemd.unit=graphical.target for setting up a graphical login screen.
For details about these special systemd boot units, view the man
What is the tool to manage services with systemd?
systemctl is the primary tool to use. It combines the functionality of both service and chkconfig into a single tool that you can use for instance to enable/disable services permanently or only for the current session.
list all running services etc:
Refer to man systemctl for more details. systemd-cgls lists the running process in a tree format. It can recursively show the content of any given control group. Refer to man systemd-cgls for more details.
How do I start/stop or enable/disable services?
Activates a service immediately:
systemctl start foo.service
Deactivates a service immediately:
systemctl stop foo.service
Restarts a service:
systemctl restart foo.service
Shows status of a service including whether it is running or not:
systemctl status foo.service
Enables a service to be started on bootup:
systemctl enable foo.service
Disables a service to not start during bootup:
systemctl disable foo.service
Check whether a service is already enabled or not:
systemctl is-enabled foo.service; echo $?
0 indicates that it is enabled, and 1 indicates that it is disabled. In Fedora 17, in addition to the return code, "enabled" or "disabled" will be printed to stdout.
Refer to man systemctl for more details.
How do I change the runlevel?
systemd has the concept of targets which is a more flexible replacement for runlevels in sysvinit.
Run level 3 is emulated by multi-user.target. Run level 5 is emulated by graphical.target. runlevel3.target is a symbolic link to multi-user.target and runlevel5.target is a symbolic link to graphical.target.
You can switch to 'runlevel 3' by running
systemctl isolate multi-user.target (or) systemctl isolate runlevel3.target
You can switch to 'runlevel 5' by running
systemctl isolate graphical.target (or) systemctl isolate runlevel5.target
How do I change the default runlevel?
Symlinks can be still used, but they were obsoleted by a built-in command to set the default target. For example, default graphical target can be set by:
systemctl enable graphical.target --force
systemd can also use symlinks to point to the default runlevel. You have to delete the existing symlink first before creating a new one
Switch to runlevel 3 by default
ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
Switch to runlevel 5 by default
ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target
systemd does not use /etc/inittab file.
How do I know the current run level?
runlevel command still works with systemd. You can continue using that however runlevels is a legacy concept in systemd and is emulated via 'targets' and multiple targets can be active at the same time. So the equivalent in systemd terms is
systemctl list-units --type=target
How to power off the machine ?
You can use
Some more possibilities are:
shutdown -P now
halt used to work the same as
poweroff in previous Fedora releases, but systemd distinguishes between the two, so
halt without parameters now does exactly what it says - it merely stops the system without turning it off.
Does service command work with systemd?
Yes. It has been modified to call systemctl automatically when dealing with systemd service files. So either of the following commands does the same thing
service NetworkManager stop
systemctl stop NetworkManager.service
Does chkconfig command work with systemd?
Yes, for turning on/off services, compatibility has been provided both ways. chkconfig has been modified to call systemctl when dealing with systemd service files. Also systemctl automatically calls chkconfig when dealing with a traditional sysv init file.
So either of the following commands does the same thing
chkconfig NetworkManager off
systemctl disable NetworkManager.service
chkconfig --list doesn't list systemd services, only Sys V services. The output of chkconfig takes note of this, along with supplying additional information.
Does system-config-services work with systemd?
Yes. It does.
How do I change the number of gettys running by default?
To add another getty:
Simply place another symlink for instantiating another getty in the getty.target.wants/ directory:
ln -sf /lib/systemd/system/getty@.service /email@example.com systemctl daemon-reload systemctl start firstname.lastname@example.org
To remove a getty:
Simply remove the getty symlinks you want to get rid of in the getty.target.wants/ directory:
rm /email@example.com /firstname.lastname@example.org systemctl daemon-reload systemctl stop email@example.com firstname.lastname@example.org
systemd does not use /etc/inittab file.
How do I set automatic login on a virtual console terminal?
First create a new service similar to getty@.service:
# cp /lib/systemd/system/getty@.service \ /etc/systemd/system/autologin@.service # ln -s /etc/systemd/system/autologin@.service \ /email@example.com
then edit ExecStart, Restart and Alias values, like this:
... ExecStart=-/sbin/mingetty --autologin USERNAME %I Restart=no ... Aliasfirstname.lastname@example.org
and finally reload daemon and start the service:
systemctl daemon-reload systemctl start email@example.com
Note that if you exit tty8 session, you wont be able to use it until next reboot or manual start by systemctl, except if you leave Restart as ‘always’, but I highly recommend to avoid this according to security reasons.
How do I customize a unit file/ add a custom unit file?
The best way to customize unit files is to add /etc/systemd/system/foobar.service.d/*.conf where foobar.service is the name of the service you want to customize. If a directory doesn't already exist, create one and drop a conf file with the settings you want to override. For example,
[Service] Restart=always RestartSec=30
Refer to man systemd.unit page for more details.
Alternatively, you can copy the distribution provided unit file from /lib/systemd/system to /etc/systemd/system since the latter has higher precedence. If a line starts with
.include followed by a file name, the specified file will be parsed at this point. Make sure that the file that is included has the appropiate section headers before any directives.You should use
.include statement instead of copying the whole unit file from /lib/systemd/system to /etc/systemd/system if possible. This will enable to update the unchanged directives correctly during future package updates.
Be careful when using
.include together with directives that can be defined multiple times (like
EnvironmentFile=), since we can only add new directives, but we can't remove already defined ones. We have to copy the whole file from /lib/systemd/system to /etc/systemd/system in this case.
Let's say we use a lighttpd server and we want to lower its niceness value. All we need to do is to add
Nice=-5 to the lighttpd.service file. We can do this by either copying the whole file from /lib/systemd/system/lighttpd.service to /etc/systemd/system/lighttpd.service or creating the following file in /etc/systemd/system/lighttpd.service:
.include /lib/systemd/system/lighttpd.service [Service] Nice=-5
How do I debug systemd issues?
Refer to How_to_debug_Systemd_problems
systemd has a built-in readahead implementation which is not enabled on upgrades. It should improve bootup speed but your mileage may vary depending on your hardware. To enable it:
systemctl enable systemd-readahead-collect.service systemctl enable systemd-readahead-replay.service
Warnings on separate /usr partition
systemd comes with extensive documentation including several man pages. The web version is at
- http://0pointer.de/blog/projects/ - Lennart's blog has lots of information about systemd. Lennart is the primary systemd developer
- Features Fedora 15:systemd
- Project homepage
- Interview with the developer