aslamnotes

Systemd Operations

1 min read

Philosophy

Everything in systemd is a unit; Unit files - defined in ini files, located under /etc/systemd/system/*.service - describes units behave.

Unit File

  • [Unit] → description + dependencies
  • [Type] section (e.g. [Service]) → how it runs
  • [Install] → enable/disable wiring, ie defines how a unit is enabled, when systemctl enable sample.service is invoked

Unit Types

  • service → start/stop a process
  • socket → listen on a socket, start service on demand
  • timer → schedule work (cron replacement)
  • mount → mount filesystems
  • target → grouping + synchronization

Install

  • WantedBy= → where this unit is hooked eg systemd’s targets
  • RequiredBy= → hard dependency
  • Alias= → alternate unit name
  • Also= → enable/disable extra units together

Sample configuration file

[Unit]
Description=Apache Tomcat Web Application Container
After=network.target
 
[Service]
Type=forking
User=tomcat
Group=tomcat
Environment="JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.362.b09-4.el9.x86_64"
Environment="CATALINA_PID=/opt/tomcat/temp/tomcat.pid"
Environment="CATALINA_HOME=/opt/tomcat"
Environment="CATALINA_BASE=/opt/tomcat"
ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/opt/tomcat/bin/shutdown.sh
RestartSec=10
Restart=always
 
[Install]
WantedBy=multi-user.target

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