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--- linux_wiki:systemd_service_script [2016/01/31 00:47]
billdozor [Implementation]
+++ linux_wiki:systemd_service_script [2018/03/23 14:52]
billdozor
@@ Line 6: / Line 6: @@
 **Checklist**
-  * Enterprise Linux 7
+  * Distro(s): Enterprise Linux 7
 ----
@@ Line 23: / Line 23: @@
   * 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.**
 ----
@@ Line 34: / Line 35: @@
 [Service]
+Type=simple
 EnvironmentFile=/etc/myprog.d/config
 ExecStart=/usr/local/bin/myprog.sh
@@ Line 41: / Line 43: @@
 WantedBy=multi-user.target
 </code>
-  * Description => Displays near the top of output on "systemctl status myprog.service"
+  * Section: Unit
-  * After => can be any valid ".target" unit
+    * Description => Displays near the top of output on "systemctl status myprog.service"
-    * See all: systemctl -t target --all
+    * After => can be any valid systemd unit (.target, .service, etc)
-  * EnvironmentFile => Configuration file to load
+      * **Multiple units are space separated**
-  * ExecStart => Executable to start
+      * Another common use target is: After=network.target
-  * Restart => Auto restarts the program if an un-handled exit error occurs
+      * See all: systemctl -t target --all
-  * WantedBy => If enabled, start under which target
+  * 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 =====
@@ Line 53: / Line 67: @@
 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>
@@ Line 65: / Line 82: @@
 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
+----