EBC Exercise 21b systemd

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thumb‎ Embedded Linux Class by Mark A. Yoder


Traditionally user space initialization has been done using init.d, however recently many distributions have been switching to systemd

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 control groups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic.

Here we'll see how to use systemd as an administration and how to create a simple service.

Administration

There are a few simple commands that show what's running under systemd and how to stop and start them. The examples here were inspired by the twenty part series on systemd administration and the three part intro by Carla Schroder

To see what's running, run

beagle$ systemctl
UNIT                        LOAD   ACTIVE SUB       DESCRIPTION
proc-sys...t_misc.automount loaded active waiting   Arbitrary Executable File Fo
sys-devi...tty-ttyO0.device loaded active plugged   /sys/devices/ocp.2/44e09000.
sys-devi...ty-ttyGS0.device loaded active plugged   /sys/devices/ocp.2/47400000.
sys-devi...-net-eth0.device loaded active plugged   /sys/devices/ocp.2/4a100000.
sys-devi...blk0boot0.device loaded active plugged   /sys/devices/ocp.2/mmc.10/mm
sys-devi...blk0boot1.device loaded active plugged   /sys/devices/ocp.2/mmc.10/mm
sys-devi...mmcblk0p1.device loaded active plugged   /sys/devices/ocp.2/mmc.10/mm
sys-devi...mmcblk0p2.device loaded active plugged   /sys/devices/ocp.2/mmc.10/mm
sys-devi...k-mmcblk0.device loaded active plugged   /sys/devices/ocp.2/mmc.10/mm
sys-devi...tty-ttyS0.device loaded active plugged   /sys/devices/platform/serial
sys-devi...tty-ttyS1.device loaded active plugged   /sys/devices/platform/serial
sys-devi...tty-ttyS2.device loaded active plugged   /sys/devices/platform/serial
sys-devi...tty-ttyS3.device loaded active plugged   /sys/devices/platform/serial
sys-module-fuse.device      loaded active plugged   /sys/module/fuse
sys-subs...ices-eth0.device loaded active plugged   /sys/subsystem/net/devices/e
-.mount                     loaded active mounted   /
dev-mqueue.mount            loaded active mounted   POSIX Message Queue File Sys
sys-fs-f...onnections.mount loaded active mounted   FUSE Control File System
sys-kernel-debug.mount      loaded active mounted   Debug File System
tmp.mount                   loaded active mounted   /tmp
systemd-...ord-console.path loaded active waiting   Dispatch Password Requests t
systemd-...ssword-wall.path loaded active waiting   Forward Password Requests to
avahi-daemon.service        loaded active running   Avahi mDNS/DNS-SD Stack
bonescript-autorun.service  loaded active running   Bonescript autorun
bonescript.service          loaded active running   Bonescript server

and so on. Look through the list and see what you recognize. If you make your window bigger you will see more information. Here's how to find more details about a given process.

beagle$ systemctl status bonescript.service
bonescript.service - Bonescript server
         Loaded: loaded (/lib/systemd/system/bonescript.service; static)
         Active: active (running) since Tue 2013-10-08 15:30:10 EDT; 1 day 20h ago
       Main PID: 346 (node)
         CGroup: name=systemd:/system/bonescript.service
       	  `-346 /usr/bin/node server.js

Oct 08 15:30:10 yoder-black-bone systemd[1]: Started Bonescript server.
Oct 08 15:30:16 yoder-black-bone bonescript[346]: [35B blob data]
Oct 08 15:30:16 yoder-black-bone bonescript[346]: - - - [Tue, 08 Oct 2013 19:...
Oct 08 15:30:17 yoder-black-bone bonescript[346]: - - - [Tue, 08 Oct 2013 19:...
Oct 08 15:30:17 yoder-black-bone bonescript[346]: - - - [Tue, 08 Oct 2013 19:...

Stopping and Starting

You can stop a process with

beagle$ systemctl | grep cloud
cloud9.service              loaded active running   Cloud9 IDE
beagle$ systemctl status cloud9
cloud9.service - Cloud9 IDE
         Loaded: loaded (/lib/systemd/system/cloud9.service; enabled)
         Active: active (running) since Fri 2000-01-07 17:46:06 EST; 13 years 9 months ago
       Main PID: 130 (node4)
         CGroup: name=systemd:/system/cloud9.service
       	  `-130 /usr/bin/node4 /usr/share/cloud9/bin/cloud9.js -l 0.0...

Oct 08 15:30:15 yoder-black-bone node4[130]: publish state{"type":"state","p...}
Oct 10 10:51:10 yoder-black-bone node4[130]: uncaught exception:
Oct 10 10:51:10 yoder-black-bone node4[130]: Error: ENOENT, No such file or ...'
Oct 10 10:51:10 yoder-black-bone node4[130]: at Object.statSync (fs.js:400:18)
Oct 10 10:51:10 yoder-black-bone node4[130]: at /usr/share/cloud9/server/clo...7
Oct 10 10:51:10 yoder-black-bone node4[130]: at Array.forEach (native)
Oct 10 10:51:10 yoder-black-bone node4[130]: at StatWatcher.<anonymous> (/us...)
beagle$ systemctl stop cloud9

Now try accessing cloud9 from a web browser (192.168.7.2:3000). It isn't there. You can start it with

beagle$ systemctl start cloud9
beagle$ systemctl status cloud9
cloud9.service - Cloud9 IDE
         Loaded: loaded (/lib/systemd/system/cloud9.service; enabled)
         Active: active (running) since Thu 2013-10-10 11:53:25 EDT; 14s ago
       Main PID: 1470 (node4)
         CGroup: name=systemd:/system/cloud9.service
       	  `-1470 /usr/bin/node4 /usr/share/cloud9/bin/cloud9.js -l 0....

Oct 10 11:53:29 yoder-black-bone node4[1470]: .){2ooooonnnnvnvnvvvvvIIIIIIll...`
Oct 10 11:53:29 yoder-black-bone node4[1470]: -{2oooonnnnnvvvvvvvlIIlllllil=...-
Oct 10 11:53:29 yoder-black-bone node4[1470]: . -."11oonnvvvnvvIIlIlliliiiii....
Oct 10 11:53:29 yoder-black-bone node4[1470]: . -+~!lvvnvIvIIllliiiii|i|||i|....
Oct 10 11:53:29 yoder-black-bone node4[1470]: . ..--~++++++++~+~+~+~+-+-+~+~....
Oct 10 11:53:29 yoder-black-bone node4[1470]: . .  . . .... . . .... .. ... ....
Oct 10 11:53:29 yoder-black-bone node4[1470]: Ajax.org Cloud9 IDE
Oct 10 11:53:29 yoder-black-bone node4[1470]: version 0.6
Oct 10 11:53:29 yoder-black-bone node4[1470]: Project root is: /var/lib/cloud9
Oct 10 11:53:29 yoder-black-bone node4[1470]: Point your browser to http://l...0

Notice the log messages have changed.

Autostart at boot time

You can use enable and disable to make a service start (or not start) at boot time.

beagle$ systemctl disable cloud9
rm '/etc/systemd/system/multi-user.target.wants/cloud9.service'
beagle$ systemctl enable cloud9
ln -s '/lib/systemd/system/cloud9.service' '/etc/systemd/system/multi-user.target.wants/cloud9.service'

Watch out though, if some other service needs the service you disabled, it will start anyway. If you want to stop a service NO MATTER WHAT.

beagle$ ln -s /dev/null /etc/systemd/system/servicename.service
beagle$ systemctl daemon-reload

systemd first looks in /etc/systemd/system and then looks in /lib/systemd/system. The command above places an empty file in /etc/systemd/system, so the real file in /lib/systemd/system is never seen.

Running your own service



thumb‎ Embedded Linux Class by Mark A. Yoder