Bureaucrats, dave_user, Administrators
8,154
edits
Changes
no edit summary
systemctl set-default multi-user
== Unit files ==
For a complete information on '''Unit''' please look to the [https://www.freedesktop.org/software/systemd/man/systemd.unit.html documentation page]
Here below you can find an extract for the main used topics and configuration descriptions.
=== Location Path ===
Units are configured by ''systemd'' using configuration files that can be found in different directories. Each of them has different priority and bahaviour:
* <code>/lib/systemd/system</code>
This directory stores a copy of configuration files. This is the default destination for new installed configuration file. Typically files in this directory should not be modified bye the user.
* <code>/etc/systemd/system</code>
This is the directory where to store a new ''Unit'' or to modify an existing one. The files present in this directory have the highest priority.
* <code>/run/systemd/system</code>
The files present in this directory have higher priority only respect the ones on <code>/lib/systemd/system</code>. Systemd creates these configuration files dinamcally at runtime; modification on this directory can be used for testing a runtime behaviour for a ''Unit'' but all modifications will be lost at next boot.
=== [Unit] section ===
This section is used for defining the metadata and relations between different ''Unit''
Please find below the main properties description:
Description=:
Name and function
Documentation=:
URI for the documentation
Requires=:
List of ''Units'' dependencies. For succesfully executing this ''Unit'', all listed dependency should be activated without errors, otherwise this Unit return ''fail''.
Wants=:
Similar to a ''Requires'' but weaker. If the ''Unit'' listed are not found or return fail, this ''Unit'' are in any case executed. this is the recommended method to be used.
BindsTo=:
Similar to ''Requires'' but it does a Sop for the ''Unit'' when the listed ''Unit'' are terminated.
Before=:
The ''Unit'' listed will not be executed until this ''Unit'' will not change to ''started''. This is used for an order of Units executions.
After=:
The ''Unit'' listed wile be started before this ''Unit''. This is used for an order of Units executions.
Conflicts=
The ''Unit'' listed cannot be executed simultaneously to this ''Unit''.
=== [Install] section ===
This section is optional but is comonly used for defining a ''Unit'' behaviour when it will be executed at boot time with ''enable'' command.
WantedBy=:
This is similar to the ''Wants='' on ''[Unit]'' section but allows to mantain the top ''Unit'' more ''clean''.
Wwhen the ''Unit'' will be enabled, a directory on <code>/etc/systemd/system</code> will be created with the ''Unit'' name adding <code>.wants</code> to the name. Inside this directotya symbolic link to the ''Unit'' is created.
Example:
* current ''Unit'' has <code>WantedBy=multi-user.target</code>
* a directory <code>/etc/systemd/system/multi-user.target.wants</code> will be created
* the symbolic link to the ''Unit'' will be created inside the new directoty
* disabling the ''Unit'' the symbolic link is deleted and the relation is then removed.
RequiredBy=:
This is similar to ''WantedBy='' but a dependency cause a ''fail'' if not satisfied. When the ''Unit'' is enabled, a directory with added ''.requires'' will be created
Also=:
When the ''Unit'' is enabled, also the listed Units are enabled too.
=== Specific sections ===
Some ''Unit'' have specific sections based on their characteristic. The most important is the section [Service] related to the Unit <code>.service</code>
Please find more information at the [https://www.freedesktop.org/software/systemd/man/systemd.service.html# documentation page]
==== [Service] section ====
Used for providing configurations for the ''services''.
===== Type =====
''Type='' should be set to :
simple:
Default configuration for a service when specified <code>ExecStarts=</code>
forking:
the process will call a <code>fork()</code> when starts causing the father to exit. This informs systemd that the process is still alive even if the father has been terminated.
oneshot:
the process has a very short execution time and then systemd should wait for its termination before continuing with other Units. this is the default configuration if ''ExecStarts='' is not specified.
dbus:
the Unit will acquire the name on the D-Bus. systemd will continue to process the other Units
notify:
the service will notify when completely initialized. Systemd will wait for the notification before continuing with the following Units
idle:
the service will not be executed until all active jobs are dispatched.
===== Other options =====
ExecStarts=:
Specifiy the full path and parameters for executing a service. If preceded by a "-" this inform that the command failure can be accepted.
ExecStartsPre=:
Può essere utilizzata per fornire comandi aggiuntivi che dovrebbero essere eseguiti prima del processo principale. Può essere usato multiple volte, deve specificare il percorso completo del comando e può essere usato anche qui il "-" per tollerare errori.
ExecReload=:
commands to be executed for reloading the service configuration.
ExecStop=:
commands required for stopping the service. If missing, the service will be killed.
ExecStopPost=:
commands to be executed after the service has been stopped..
RestartSec=:
time to sleep (seconds) before restarting the service.
Restart=:
restart conditions for systemd to be checked before restarting the service (if terminated). Can be set to "always","on-success", "on-failure", "on-abnormal", "on-abort", or "on-watchdog".
TimeoutSec=:
time to sleep during ''start'' or ''stop'' before considering the process failed on start or stop. Start and stop timeout can be set with different values using <code>TimeoutStartSec=</code> nad e <code>TimeoutStopSec=</code>
