Systemd Service Script

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General Information

Creating a systemd until file (service script).

Checklist

Distro(s): Enterprise Linux 7

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

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.

[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

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.