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HowTo
start / stop
systemctl daemon-reload
systemctl start servicename
info/status
# systemctl get-default
multi-user.target
systemd-analyze blame
systemd-analyze critical-chain
systemd-analyze critical-chain network.service
systemctl list-dependencies network.service
systemctl --failed
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:
systemd.unit=emergency
systemd.log_level=debug systemd.log_target=console console=ttyS0,38400
Enable in u-boot:
setenv bootargs ${bootargs} systemd.unit=emergency.target
Enable debug console on tty9
systemctl enable debug-shell.service
Start service when MMC card is inserted
Create directory “dev-mmcblk0.device.wants” and put symlink to service inside it. List of devices:
systemctl --all --full -t device
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 allExecStartPre=
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
- /etc/systemd/system/getty@tty1.service.d/noclear.conf
[Service] TTYVTDisallocate=no
udev
In udev rules.d add TAG+=“systemd”:
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"
And now device is visible from systemd:
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
You can create refer to device, e.g. create .wants directory
/etc/systemd/system/ev-input-lcd_sandwich_touchscreen.device.wants
udev: start service
To start service if device is inserted:
- mu.rule
..., TAG+="systemd", ENV{SYSTEMD_WANTS}="netctl-auto@mywifi.service"
do not mount crypted volumes
After switching to systemd by command
apt-get install systemd-sysv
, 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:
- /etc/crypttab
/MyMountPoint /dev/vg_MyName/lv_MyName none luks,noauto,noearly
Debian: Set network service timeout
System startup can hang forever if there is no link on ethernet cable:
[ **] A start job is running for LSB: Raise network interf...38s / no limit)
To set timeout, add file:
- /etc/systemd/system/networking.service.d/reduce-timeout.conf
[Service] TimeoutStartSec=15