(drop the section on tools. systemd ui has been retired and the section itself is outdated)
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== Boot Kernel Command Line ==
== Boot Kernel Command Line ==
Revision as of 15:47, 9 April 2015
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://www.youtube.com/watch?v=TyMLi8QF6sw
- 1 Why systemd?
- 2 systemd documentation
- 3 Boot Kernel Command Line
- 4 What is the tool to manage services with systemd?
- 5 How do I start/stop or enable/disable services?
- 6 How do I change the target (runlevel) ?
- 7 How do I change the default target?
- 8 How do I know the current target?
- 9 How to power off the machine ?
- 10 Does service command work with systemd?
- 11 Does chkconfig command work with systemd?
- 12 Does system-config-services work with systemd?
- 13 How do I change the number of gettys running by default?
- 14 How do I set automatic login on a virtual console terminal?
- 15 How do I customize a unit file/ add a custom unit file?
- 16 How do I debug systemd issues?
- 17 Man pages
- 18 References
systemd has very comprehensive documentation. Refer to
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
Deactivates a service immediately:
systemctl stop foo
Restarts a service:
systemctl restart foo
Shows status of a service including whether it is running or not:
systemctl status foo
Enables a service to be started on bootup:
systemctl enable foo
Disables a service to not start during bootup:
systemctl disable foo
Prevent a service from starting dynamically or even manually unless unmasked:
systemctl mask foo
Check whether a service is already enabled or not:
systemctl is-enabled foo
Refer to man systemctl for more details.
How do I change the target (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
You can switch to 'runlevel 5' by running
systemctl isolate graphical.target
How do I change the default target?
systemctl set-default <name of target>.target
graphical.target is the default. You might want multi-user.target for the equivalent of non graphical (runlevel 3) from sysv init. The full list of targets can be accessed via systemctl list-units --type=target
systemd does not use /etc/inittab file.
How do I know the current 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
systemctl stop NetworkManager
service NetworkManager stop
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
systemctl disable NetworkManager
chkconfig NetworkManager off
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?
The simplest way is to edit /etc/systemd/logind.conf (man page):
[Login] ... NAutoVTs=8
This setting will take effect after reboot.
Alternatively, getty@.services which open the login prompt can be enabled and started individually.
To add another getty:
systemctl enable getty@tty8 systemctl start getty@tty8
To remove a getty:
systemctl disable getty@tty8 systemctl stop getty@tty8
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.
Special care must be taken when overriding options which can be set muliple times (
ExecStartPost are a common example). Assigning some value to the option appends to the existing list, while assiging the empty value resets the list.
For example, let's say we have a service file like this:
[Service] ExecStart=/bin/echo execstart1 ExecStart= ExecStart=/bin/echo execstart2 ExecStartPost=/bin/echo post1 ExecStartPost=/bin/echo post2
When started, this service will print
execstart2 post1 post2
The same rules apply to snippets in
.d directories. This means that snippets which override
ExecStart and similar settings, often should start with the empty assignment
ExecStart=, followed by the new setting.
How do I debug systemd issues?
Refer to How_to_debug_Systemd_problems
systemd comes with extensive documentation including several man pages.
- Project homepage
- http://0pointer.de/blog/projects/ - Lennart's blog has lots of information about systemd. Lennart is the primary systemd developer
- Features Fedora 15:systemd
- Interview with the developer