====== 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<code bash>systemctl start <name-of-service></code>
    * **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 ======

<code bash 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
</code>
  * 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

----

===== Example: Test Script =====

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
<code bash>
#!/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
</code>
  * **Note: Ensure this script is executable, or the service will fail to start.**

----

==== Example: Service Status ====

<code bash>
[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
</code>

----

==== Example: Logs ====

<code bash>
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...
</code>

----

===== Example: Docker Compose =====

Putting docker-compose commands into a service.

/etc/systemd/system/docker-compose.service
<code bash>
[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
</code>

----

===== Example: Apache HTTPD Compiled =====

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

\\
/etc/systemd/system/httpd-local.service
<code bash>
[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
</code>

\\
Reload systemd<code bash>systemctl daemon-reload</code>

\\
Enable/start service<code bash>systemctl enable httpd-local
systemctl start httpd-local</code>

----

====== 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/

===== Override Example: docker service =====

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)<code bash>mkdir /etc/systemd/system/docker.service.d/</code>
  * Create the over ride file<code bash>/etc/systemd/system/docker.service.d/docker.conf

[Service]
EnvironmentFile=
EnvironmentFile=-/etc/sysconfig/docker
ExecStart=
ExecStart=/usr/bin/dockerd $OPTIONS</code>
    * 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<code bash>systemctl daemon-reload</code>

  * Restart the service

===== Override Example: rpcbind 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)<code bash>mkdir /etc/systemd/system/rpcbind.service.d/</code>
  * Create the over ride file (NAME.conf)<code bash>/etc/systemd/system/rpcbind.service.d/rpcbind.conf

[Service]
ExecStart=
ExecStart=/sbin/rpcbind $RPCBIND_ARGS</code>
    * 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<code bash>systemctl daemon-reload</code>

  * Restart the service

----