[[linux_wiki:systemd_service_script]]

Systemd Service Script

General Information

Creating a systemd until file (service script).

Checklist

  • Distro(s): Enterprise Linux 7

Unit File Reference

  • /usr/lib/systemd/system ⇒ system unit configuration files (default with system)
  • /etc/systemd/system ⇒ additional configuration files (downloaded or custom)

Implementation

  • Download the code
  • Modify each section to make sense for your service
  • Copy to /etc/systemd/system/<name-of-service>.service
  • Start your service
    systemctl start <name-of-service>
    • Note: This will fail if the ExecStart script/program does not have the executable permissions or if the EnvironmentFile config file does not exist.

The Service Unit File

myprog.service
[Unit]
Description=My Awesome Program
After=syslog.target
 
[Service]
Type=simple
EnvironmentFile=/etc/myprog.d/config
ExecStart=/usr/local/bin/myprog.sh
Restart=on-abort
 
[Install]
WantedBy=multi-user.target
  • Section: Unit
    • Description ⇒ Displays near the top of output on “systemctl status myprog.service”
    • After ⇒ can be any valid systemd unit (.target, .service, etc)
      • Multiple units are space separated
      • Another common use target is: After=network.target
      • See all: systemctl -t target –all
  • Section: Service
    • Type ⇒ The process and daemon behavior
      • simple → default if Type is not set, but ExecStart is. Main process specified in ExecStart line.
      • forking → service forks a child process and the parent process exits
      • oneshot → default if Type and ExecStart are not set. Process is short lived, systemd will wait for the process to exit before continuting with other units.
      • notify → service will issue a notification when it has finished starting. Systemd will wait before processing other units
    • EnvironmentFile ⇒ Configuration file to load
    • ExecStart ⇒ Executable to start
    • Restart ⇒ Auto restarts the program if an un-handled exit error occurs
  • Section: Install
    • WantedBy ⇒ If enabled, start under which target

This is the script that was used to test the custom systemd service unit file.

NOTE: The script being launched MUST have the “#!/bin/bash” line first or the unit file will fail. (Cannot have a standard comment line as the first line)


/usr/local/bin/myprog.sh

#!/bin/bash
 
echo "Welcome to my program"
logger -p info "$0 has started on $(date)"
 
while true; do
  logger -p info "$0 is still running..."
  sleep 30
done
  • Note: Ensure this script is executable, or the service will fail to start.

[root@server1 system]# systemctl start myprog.service
[root@server1 system]# systemctl status myprog.service 
● myprog.service - My Awesome Program
   Loaded: loaded (/etc/systemd/system/myprog.service; disabled; vendor preset: disabled)
   Active: active (running) since Sun 2016-01-24 10:30:08 CST; 6s ago
 Main PID: 17602 (myprog.sh)
   CGroup: /system.slice/myprog.service
           ├─17602 /bin/bash /usr/local/bin/myprog.sh
           └─17608 sleep 30
 
Jan 24 10:30:08 server1.local systemd[1]: Started My Awesome Program.
Jan 24 10:30:08 server1.local systemd[1]: Starting My Awesome Program...
Jan 24 10:30:08 server1.local myprog.sh[17602]: Welcome to my program

journalctl -f
-- Logs begin at Fri 2015-12-25 22:36:05 CST. --
Jan 24 10:30:08 server1.local systemd[1]: Starting My Awesome Program...
Jan 24 10:30:08 server1.local myprog.sh[17602]: Welcome to my program
Jan 24 10:30:08 server1.local logger[17605]: /usr/local/bin/myprog.sh has started on Sun Jan 24 10:30:08 CST 2016
Jan 24 10:30:08 server1.local logger[17606]: /usr/local/bin/myprog.sh is still running...
Jan 24 10:30:38 server1.local logger[17683]: /usr/local/bin/myprog.sh is still running...
Jan 24 10:31:08 server1.local logger[17693]: /usr/local/bin/myprog.sh is still running...

Putting docker-compose commands into a service.

/etc/systemd/system/docker-compose.service

[Unit]
Description=Docker Compose Containers
Requires=docker.service
After=docker.service
 
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/bin/docker-compose -f /data/docker/docker-compose.yml up -d
ExecStop=/usr/local/bin/docker-compose -f /data/docker/docker-compose.yml down
 
[Install]
WantedBy=multi-user.target

Creating a service unit file for a locally compiled and installed Apache web server.


/etc/systemd/system/httpd-local.service

[Unit]
Description=Apache Web Server
After=network.target remote-fs.target nss-lookup.target
 
[Service]
Type=forking
PIDFile=/usr/local/apache2/logs/httpd.pid
ExecStart=/usr/local/apache2/bin/apachectl start
ExecStop=/usr/local/apache2/bin/apachectl graceful-stop
ExecReload=/usr/local/apache2/bin/apachectl graceful
PrivateTmp=true
LimitNOFILE=infinity
 
[Install]
WantedBy=multi-user.target


Reload systemd

systemctl daemon-reload


Enable/start service

systemctl enable httpd-local
systemctl start httpd-local

Override File

Override files are used when you want to modify part or all of a RPM/system provided systemd unit file. Use over rides instead of directly modifying system unit files, as they could be reverted upon next related package update.

System Provided unit files: /usr/lib/systemd/system/

System provided file to over ride: /usr/lib/systemd/system/docker.service

  • Create a directory to contain the over ride file (named after the original unit file name)
    mkdir /etc/systemd/system/docker.service.d/
  • Create the over ride file
    /etc/systemd/system/docker.service.d/docker.conf
     
    [Service]
    EnvironmentFile=
    EnvironmentFile=-/etc/sysconfig/docker
    ExecStart=
    ExecStart=/usr/bin/dockerd $OPTIONS
    • Each variable with a blank assignment ('EnvironmentFile=') clears that variable. If you did not put the assignment to nothing line, the variables would be appended to the built in values.
  • Reload the systemd daemon for the override file to be picked up
    systemctl daemon-reload
  • Restart the service

System provided file to over ride: /usr/lib/systemd/system/rpcbind.service

  • Create a directory to contain the over ride file (named after the original unit file name, but add a “.d” for directory)
    mkdir /etc/systemd/system/rpcbind.service.d/
  • Create the over ride file (NAME.conf)
    /etc/systemd/system/rpcbind.service.d/rpcbind.conf
     
    [Service]
    ExecStart=
    ExecStart=/sbin/rpcbind $RPCBIND_ARGS
    • Each variable with a blank assignment ('EnvironmentFile=') clears that variable. If you did not put the assignment to nothing line, the variables would be appended to the built in values.
  • Reload the systemd daemon for the override file to be picked up
    systemctl daemon-reload
  • Restart the service

  • linux_wiki/systemd_service_script.txt
  • Last modified: 2019/05/26 03:50
  • (external edit)