= Systemd

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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

[[why-systemd]]
Why systemd?
~~~~~~~~~~~~

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

[[systemd-documentation]]
systemd documentation
~~~~~~~~~~~~~~~~~~~~~

systemd has very comprehensive documentation. Refer to

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

[[boot-kernel-command-line]]
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

[[what-is-the-tool-to-manage-services-with-systemd]]
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.

[[how-do-i-startstop-or-enabledisable-services]]
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]]
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]]
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 do I know the current target?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

....
 systemctl get-default 
....

[[how-to-power-off-the-machine]]
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.

[[does-service-command-work-with-systemd]]
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 
....

[[does-chkconfig-command-work-with-systemd]]
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.

[[does-system-config-services-work-with-systemd]]
Does system-config-services work with systemd?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Yes. It does.

[[how-do-i-change-the-number-of-gettys-running-by-default]]
How do I change the number of gettys running by default?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The simplest way is to edit /etc/systemd/logind.conf
([http://www.freedesktop.org/software/systemd/man/logind.conf.html#NAutoVTs=
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]]
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.

[[how-do-i-customize-a-unit-file-add-a-custom-unit-file]]
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
http://www.freedesktop.org/software/systemd/man/systemd.unit.html[systemd.unit]
page for more details.

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.

[[how-do-i-debug-systemd-issues]]
How do I debug systemd issues?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Refer to How_to_debug_Systemd_problems

[[man-pages]]
Man pages
---------

systemd comes with extensive documentation including several man pages.

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
----------

* http://www.freedesktop.org/wiki/Software/systemd[Project homepage]
* http://0pointer.de/blog/projects/ - Lennart's blog has lots of
information about systemd. Lennart is the primary systemd developer
* http://www.freedesktop.org/wiki/Software/systemd/FrequentlyAskedQuestions
* http://www.freedesktop.org/wiki/Software/systemd/TipsAndTricks
* link:Features/systemd[ Features Fedora 15:systemd]
* http://fosdem.org/2011/interview/lennart-poettering.html[Interview
with the developer]
'''

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