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--- linux_wiki:systemd_service_script [2018/03/23 14:52]
billdozor
+++ linux_wiki:systemd_service_script [2019/05/25 23:50]
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-====== 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>
-----
-====== 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
-----