Systemd

From FedoraProject

(Difference between revisions)
Jump to: navigation, search
m (Spelling and grammar corrections)
(drop the section on tools. systemd ui has been retired and the section itself is outdated)
 
(8 intermediate revisions by 2 users not shown)
Line 1: Line 1:
 
{{autolang|base=yes}}
 
{{autolang|base=yes}}
  
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
+
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
  
 
{{admon/note|For system administrators|  
 
{{admon/note|For system administrators|  
Line 15: Line 15:
  
 
http://0pointer.de/blog/projects/systemd-docs.html
 
http://0pointer.de/blog/projects/systemd-docs.html
 
== Tools ==
 
 
* <code>systemctl</code>: used to introspect and control the state of the systemd system and service manager
 
* <code>systemd-cgls</code>: recursively shows the contents of the selected Linux control group hierarchy in a tree
 
* <code>systemadm</code>: a graphical frontend for the systemd system and service manager that allows introspection and control of systemd.  Part of the systemd-gtk package.  This is an 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 ==
 
== Boot Kernel Command Line ==
Line 71: Line 63:
 
<pre> systemctl disable foo </pre>  
 
<pre> systemctl disable foo </pre>  
  
Check whether a service is already enabled or not:
+
Prevent a service from starting dynamically or even manually unless unmasked:
 +
 
 +
<pre> systemctl mask foo </pre>
  
<pre> systemctl is-enabled foo; echo $? </pre>
+
Check whether a service is already enabled or not:
  
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.
+
<pre> systemctl is-enabled foo</pre>
  
 
Refer to man systemctl for more details.
 
Refer to man systemctl for more details.
Line 146: Line 140:
 
== How do I change the number of gettys running by default? ==
 
== How do I change the number of gettys running by default? ==
  
To add another getty:
+
The simplest way is to edit /etc/systemd/logind.conf ([http://www.freedesktop.org/software/systemd/man/logind.conf.html#NAutoVTs= man page]):
  
Simply place another symlink for instantiating another getty in the getty.target.wants/ directory:
+
<pre>
 +
[Login]
 +
...
 +
NAutoVTs=8
 +
</pre>
  
 +
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:
 
<pre>
 
<pre>
ln -sf /lib/systemd/system/getty@.service /etc/systemd/system/getty.target.wants/getty@tty9.service
+
systemctl enable getty@tty8
systemctl daemon-reload
+
systemctl start getty@tty8
systemctl start getty@tty9.service
+
 
</pre>
 
</pre>
  
 
To remove a getty:
 
To remove a getty:
 
Simply remove the getty symlinks you want to get rid of in the getty.target.wants/ directory:
 
  
 
<pre>
 
<pre>
rm /etc/systemd/system/getty.target.wants/getty@tty5.service /etc/systemd/system/getty.target.wants/getty@tty6.service
+
systemctl disable getty@tty8
systemctl daemon-reload
+
systemctl stop getty@tty8
systemctl stop getty@tty5.service getty@tty6.service
+
 
</pre>
 
</pre>
  
Line 204: Line 203:
  
 
<pre>
 
<pre>
 
 
[Service]
 
[Service]
 
Restart=always
 
Restart=always
 
RestartSec=30
 
RestartSec=30
 
 
</pre>
 
</pre>
  
Refer to man systemd.unit page for more details.  
+
Refer to man [http://www.freedesktop.org/software/systemd/man/systemd.unit.html 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 <code>.include</code> 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 <code>.include</code> 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.
+
{{admon/tip| Don't forget to reload systemd daemon using <code>systemctl daemon-reload</code> and <code> systemctl restart foobar</code> after editing a unit file where foobar is the name of the unit. Also note that you can <code> systemd-delta </code> to list the unit files which have been customized and also the precise differences }}
  
Be careful when using <code>.include</code> together with directives that can be defined multiple times (like <code>EnvironmentFile=</code>), 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.
+
Special care must be taken when overriding options which can be set muliple times (<code>ExecStart</code>, <code>ExecStartPre</code>, <code>ExecStartPost</code> are a common example). Assigning some value to the option ''appends'' to the existing list, while assiging the ''empty'' value ''resets'' the list.
 
+
Let's say we use a lighttpd server and we want to lower its niceness value. All we need to do is to add <code>Nice=-5</code> 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:
+
  
 +
For example, let's say we have a service file like this:
 
<pre>
 
<pre>
.include /lib/systemd/system/lighttpd.service
 
 
[Service]
 
[Service]
Nice=-5
+
ExecStart=/bin/echo execstart1
 +
ExecStart=
 +
ExecStart=/bin/echo execstart2
 +
ExecStartPost=/bin/echo post1
 +
ExecStartPost=/bin/echo post2
 +
</pre>
 +
When started, this service will print
 +
<pre>
 +
execstart2
 +
post1
 +
post2
 
</pre>
 
</pre>
  
{{admon/tip| Don't forget to reload systemd daemon using <code>systemctl daemon-reload</code> and <code> systemctl restart foobar</code> after editing a unit file where foobar is the name of the unit.  Also note that you can <code> systemd-delta </code> to list the unit files which have been customized and also the precise differences }}
+
The same rules apply to snippets in <code>.d</code> directories. This means that snippets which override
 
+
<code>ExecStart</code> and similar settings, often should start with the empty assignment <code>ExecStart=</code>, followed by the new setting.
{{admon/note|When modifying an unit that has an symlink pointing to that unit for example like the display-manager.service -> prefdm.service does, the symlink should be copied instead of the actual unit (ie) display-manager.service should be copied to the /etc/systemd/system directory or a new unit created with .includes that bears that name .}}
+
  
 
== How do I debug systemd issues? ==
 
== How do I debug systemd issues? ==
Line 235: Line 239:
 
= Man pages =
 
= Man pages =
  
systemd comes with extensive documentation including several man pages. The web version is at
+
systemd comes with extensive documentation including several man pages.
  
http://www.freedesktop.org/software/systemd/man/
+
On the web: [http://www.freedesktop.org/software/systemd/man/ list of all systemd man pages],
 +
[http://www.freedesktop.org/software/systemd/man/systemd.directives.html index of all settings].
  
 
= References =
 
= References =

Latest 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

Note.png
For system administrators
System administrators can visit this page, to understand how to use the native systemctl calls that replace their old workflow in SysVinit. Note that the service and chkconfig commands will continue to work as expected in the systemd world.

Contents

[edit] Why systemd?

http://0pointer.de/blog/projects/why.html

[edit] systemd documentation

systemd has very comprehensive documentation. Refer to

http://0pointer.de/blog/projects/systemd-docs.html

[edit] 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 systemd.special page. it scripts

[edit] 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:

 systemctl 

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.

[edit] 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.

[edit] 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 

[edit] 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.

[edit] How do I know the current target?

 systemctl get-default 

[edit] How to power off the machine ?

You can use

 poweroff 

Some more possibilities are: halt -p, init 0, shutdown -P now

Note that 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.

[edit] 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 

(or)

 service NetworkManager stop 

[edit] 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 

(or)

 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.

[edit] Does system-config-services work with systemd?

Yes. It does.

[edit] 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.

[edit] 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 \
        /etc/systemd/system/getty.target.wants/getty@tty8.service

then edit ExecStart, Restart and Alias values, like this:

...
ExecStart=-/sbin/mingetty --autologin USERNAME %I
Restart=no
...
Alias=getty.target.wants/getty@tty8.service

and finally reload daemon and start the service:

systemctl daemon-reload
systemctl start getty@tty8.service

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.

[edit] 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,

/etc/systemd/system/httpd.service.d/restart.conf

[Service]
Restart=always
RestartSec=30

Refer to man systemd.unit page for more details.

Idea.png
Don't forget to reload systemd daemon using systemctl daemon-reload and systemctl restart foobar after editing a unit file where foobar is the name of the unit. Also note that you can systemd-delta to list the unit files which have been customized and also the precise differences

Special care must be taken when overriding options which can be set muliple times (ExecStart, ExecStartPre, 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.

[edit] How do I debug systemd issues?

Refer to How_to_debug_Systemd_problems

[edit] Man pages

systemd comes with extensive documentation including several man pages.

On the web: list of all systemd man pages, index of all settings.

[edit] References