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Starting from [[Axel_Embedded_Linux_Kit_(XELK)#XELK_4.0.0|XELK 4.0.0]] the root file system generated by NXP Yocto recipes produces a root file system using [https://www.freedesktop.org/wiki/Software/systemd/ systemd].
{{ImportantMessage|text=This application note '''is not a complete systemd user's guide''' but collects some useful hints that can be used for getting familiar with Systemdsystemd. There is a plenty of documentation and User's Guide available for systemd, but some simple example examples - that can be found here below - may simplify the systemd approach for beginners.}}
== Brief description Architecture ==Systemd manages not only services but many different objects called '''Unit'''. Unit are related to the resources that systemd can manage. Unit configurations are defined into the ''Unit files''.
It is possible to display all '''started''' services with the following userspace command:
systemctl -t service --all
=== Other useful = service commands ====
Starting a service from userspace:
systemctl disable ''<service_name>''
== Targets == mask a service ====
<pre>
</pre>
=== Active targets == restart =====
=== Location Path Configuring the network interfaces===
{| class=== Specific sections ==="wikitable"|-! Value !! Keyword |-| 0 || emerg |-| 1 || alert |-| 2|| crit |-| 3|| err |-| 4|| warning |-| 5|| notice |-| 6|| info |-| 7|| debug |}''<time>''User can filter by arbitrary time limits using the <code>--since</code> and <code>--until</code> options, which restrict the entries displayed to those after or before the given time, respectively. E.g.:
For displaying the log related to a user ID, use <code>Type_UID=</code> uses one of the (main) following values:parameter
==== Target and ExecStopPostrunlevels ====:
<pre>
</pre>
===== Basic settings =Active targets ====
{| class===== running "wikitable"|-! Path !! Description|-| <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 by 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 dinamically at runtime; modification on this directory can be used for testing a runtime behaviour for a service =====''Unit'' but all modifications will be lost at next boot.|}
=== From SystemV to Systemd = [Install] section options ====
* current ''Unit'' has <code>WantedBy==== restart ====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 directory* disabling the ''Unit'' the symbolic link is deleted and the relation is then removed.
==== stop = [Service] section =====
<precode>stop() { echo "Stopping My Custom Service..." /usr/bin/myservice shutdown}Type=</precode>uses one of the (main) following values:
{| class="wikitable"|-! Value !! Description|-| ExecStarts= Network Configuration : || Specifiy the full path and parameters for executing a service. If preceded by a "-" this inform that the command failure can be accepted.|-| ExecStartsPre=: || used for adding more commands to be executed before starting the main process. May be used multiple times specifying the complete path and command parameters.|-| 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> and <code>TimeoutStopSec=</code>|}
/etc/systemd/networksystem/eth0''<service_name>''.networkservice
The following paragraph shows how to create a new service called <code>iperf3</precode>executing the iperf3 command in server mode
<pre>
[Install]
WantedBy=multi-user.target
</pre>
{| class="wikitable"|-! Parameter !! Description|-| After || The executed command (''iperf3'') requires the network interface to be already active, so we use <precode>After</code> for this purpose.ctrl_interface=/var/|-| Restart || This is configured with ''0'' for disabling the service after it has been run/wpa_supplicant.|-| RestartSec || time sleep before restarting the service; default value is 100ms.|-| User || configures the ''user'' or ''group'' used for executing the service.|-| ExecStart || command to be executed when the service will be started (in our case ''iperf3'').eapol_version=1|-ap_scan=1| WantedBy || defines which target is used related to the service started. fast_reauth=1|}
systemctl enable wpa_supplicant@wlan0iperf3