====== systemd ======

  * [[https://www.freedesktop.org/software/systemd/man/latest/bootup.html|bootup — System bootup process]]

===== HowTo =====
==== start / stop ====
Rerun all generators, reload all unit files and recreate dependency tree:
<code bash>
systemctl daemon-reload
</code>

<code bash>
systemctl start servicename
</code>

==== info/status ====
<code bash>
# systemctl get-default
multi-user.target
</code>

<code bash>
systemd-analyze blame
systemd-analyze critical-chain
systemd-analyze critical-chain  network.service
systemctl list-dependencies network.service
systemctl --failed
</code>

<code bash>
systemd-cgtop
</code>

==== emergency mode  ====
=== Prevent services from running ===
If services are defined with **DefaultDependencies=no**, they will be started unconditionally even in emergency mode, wchich can be wrong.

=== If mount fails ===
**local-fs.target** is configured to go to **OnFailure=emergency.target**.
File /etc/fstab is parsed by **systemd-fstab-generator** to generate .mount units, which are **Required**.

To let mounts fail without switching to emergency mode, special attribute are introduced to fstab.
[[http://www.freedesktop.org/software/systemd/man/systemd.mount.html]]

==== Debug ====
Kernel commandline:

<code>systemd.unit=emergency</code>

<code>systemd.log_level=debug systemd.log_target=console console=ttyS0,38400</code>

Enable in u-boot:
<code>setenv bootargs ${bootargs} systemd.unit=emergency.target</code>

Enable debug console on tty9
<code bash>systemctl enable debug-shell.service</code>

==== Start service when MMC card is inserted ====
Create directory "dev-mmcblk0.device.wants" and put symlink to service inside it.
List of devices: <code bash>systemctl --all --full -t device</code>

==== Configuration ====

=== DefaultDependencies ===
Value for unit **DefaultDependencies** is set to **yes** by default.
it will add following dependencies:
  * **Conflicts=shutdown.target** to stop service during shutdown
  * **Conflicts=umount.target** to umount mounts durign shutdown
  * **Requires=basic.target** and **After=basic.target**

=== Unit Types ===
  * .service plain service - for running daemons
  * .socket  socket listeners - like inetd
  * .device
  * .path    filesystem triggers (when file is changed)
  * .mount
  * .automount
  * .swap
  * .target
  * .timer
  * .snapshot
  * .slice
  * .scope

=== [Unit] ===
  * Requires  - units listed here, are also activated with unit. If any start fail, this unit will be not activated.
  * Conflicts - negative dependencies, opposite to Requires

  * Requisite - similar to require, but if not met, service will be not started (fail immediately). Usefull to perform action when removable device is inserted. 
  * Requisite=!local-fs.target

  * BindsTo - similar to require, but also declares to stop unit when other units dissapers (aslo nice for removable devices handling)
  * PartOf - stops/starts unit when unit listed is stopped/started

  * After - start service after other services are started completely.
  * Before


=== [Service] ===
  * Type
    * Type=simple  - default -
    * Type=forking - process will spawn child and exit. Child should live as daemon.
      * PIDFile=/var/run/service.pid - set it to give systemd possibility to known forked child PID
    * Type=oneshot - process should exit. Systemd is not waiting for finish. Like batch file.
      * usefull for setup some things, not starting daemons. See ''ReamainAfterExit=Yes'')
      * Multiple ExecStart= allowed, and will be executed sequentially
    * Type=dbus    - systemd assume process started when process name connects to D-Bus
    * Type=notify  - systemd assume process started when process explicitly notify systemd using ''sd_notify()''
    * Type=idle


  * ExecStart= - first argument MUST be full path to executable
    * ExecStart=-/bin/false   - minus sign = ignore exit code and assume always success
    * Multple ExecStart= are allowed, and executed sequentially. If one command fails, other lines are not executed and unit is failed.
  * ExecStartPre= - ''ExecStart='' will run only if all ''ExecStartPre='' command exits with success. May not to start long processes.
  * ExecStartPost= - will be executed only if service has started successfully
  * ExecStop=
  * ExecReload=

  * Nice=-20
  * IOSchedulingClass=0
  * IOSchedulingPriority=0
  * StandardOutput=tty |none | journal+console

  * Restart=always
  * RestartSec=10s

  * RemainAfterExit=Yes - keep service active status, even all process exits. usefull for ''Type=oneshot''


==== tricks ====
Condition doesn't skip service, but only service is not started but all requirements (after,before, wants, conflicts) works. So Service is not started but it is still disabling other services by Conflicts definition.
If service is not started by Condtiion it is still conflicting 

=== Remove startup console clearing ===
<file | /etc/systemd/system/getty@tty1.service.d/noclear.conf>

[Service]
TTYVTDisallocate=no
</file>

=== udev ===
In udev rules.d add TAG+="systemd":
<code>
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", ATTRS{name}=="edt-ft53*", \
    SYMLINK+="input/lcd_sandwich_touchscreen input/touchscreen_edt", \
    TAG+="systemd", \
    OPTIONS+="link_priority=100"
</code>
And now device is visible from systemd:
<code bash>
systemctl -l -a
  dev-input-event0.device                                                                        loaded    active   plugged   /dev/input/event0
  dev-input-lcd_sandwich_touchscreen.device                                                      loaded    active   plugged   /dev/input/lcd_sandwich_touchscreen
</code>
You can create refer to device, e.g. create .wants directory
<code>/etc/systemd/system/ev-input-lcd_sandwich_touchscreen.device.wants</code>

=== udev: start service ===
To start service if device is inserted:
<file | mu.rule>
..., TAG+="systemd", ENV{SYSTEMD_WANTS}="netctl-auto@mywifi.service"
</file>

=== do not mount crypted volumes ===
After switching to systemd by command <code bash>apt-get install systemd-sysv</code>, new problem occurs: 
system boot stops and waits for password for encrypted partition (with user data - no needed to system start).

To prevent automount of crypted volumes, additional parameters 'noauto' and 'noearly' must be added to /etc/crypttab:
<file | /etc/crypttab>
/MyMountPoint		/dev/vg_MyName/lv_MyName	none	luks,noauto,noearly
</file>

=== Debian: Set network service timeout ===
System startup can hang forever if there is no link on ethernet cable:
<code>[    **] A start job is running for LSB: Raise network interf...38s / no limit)</code>
To set timeout, add file:
<file | /etc/systemd/system/networking.service.d/reduce-timeout.conf>
[Service]
TimeoutStartSec=15
</file>

====== Issues ======

===== init.d services not started =====

<code>
systemd-sysv-generator[320]: stat() failed on /etc/init.d/traccar, ignoring: No such file or directory
systemd-sysv-generator[320]: stat() failed on /etc/init.d/ts3server, ignoring: No such file or directory
systemd-sysv-generator[320]: stat() failed on /etc/init.d/miio_server, ignoring: No such file or directory
</code>

Reason is that some init scripts are symlinked to files located in **/opt** directory, which is a different FS (in this case BTRFS subvolume), and it was not mounted when **systemd-sysv-generator** was started.

**Solution:**
[[https://access.redhat.com/solutions/3094591|How to mount non-root filesystem before systemd-sysv-generator runs?]]

> Under systemd-enabled systems, there's a new-with-systemd mount-option you can place in ''/etc/fstab'' — **x-initrd.mount**. 
> You also need to make sure that your filesystem's fs_passno is set to "0" ...and if your filesystem lives on an LVM2 volume, you need to update your GRUB2 config to ensure that the LVM gets onlined prior to systemd invoking the systemd-sysv-generator utility