#atom

Configuration system for managing Linux service processes, dependencies, and behaviors

Core Idea: Systemd service units are configuration files that define how applications run as system services, including startup behavior, environment variables, dependencies, and resource controls, enabling reliable process management on Linux systems.

Key Elements

• Unit File Structure

  • [Unit] section: Description, dependencies, ordering
  • [Service] section: Execution, restart, user/group settings
  • [Install] section: Activation targets and enablement
  • File naming convention: servicename.service
  • Storage location: /etc/systemd/system/ or /usr/lib/systemd/system/

• Service Types

  • simple: Default type, main process is the executed process
  • forking: Process forks, parent exits, child continues
  • oneshot: Executes and exits
  • notify: Process sends notification when ready
  • dbus: Process acquires a D-Bus name when ready
  • idle: Delayed start until system is less busy

• Key Directives

  • ExecStart: Command to execute when service starts
  • User/Group: Which user/group runs the service
  • WorkingDirectory: Service working directory
  • Environment: Environment variable definitions
  • Restart: Restart behavior (always, on-failure, etc.)
  • RestartSec: Time to wait before restart
  • After/Before: Ordering relative to other units
  • Requires/Wants: Dependency definitions

• Implementation Example

  # /usr/lib/systemd/system/application@.service
  [Unit]
  Description=Application Service
  After=network.target postgresql.service
  
  [Service]
  Type=simple
  User=%i
  WorkingDirectory=/home/%i/application/
  ExecStart=/home/%i/go/bin/application
  Restart=on-failure
  RestartSec=5s
  
  [Install]
  WantedBy=multi-user.target
  

- **Management Commands**
    - `systemctl start|stop|restart service`: Control service state
    - `systemctl enable|disable service`: Control autostart
    - `systemctl status service`: Check service status
    - `systemctl daemon-reload`: Reload systemd configuration
    - `journalctl -u service`: View service logs

## Connections

- **Related Concepts**: Linux Service Management (broader concept), Process Supervision (general approach), Init Systems (historical context)
- **Broader Context**: Linux System Administration (domain)
- **Applications**: VPS CI/CD Pipeline (implementation component), Go Application Deployment (use case)
- **Components**: Systemd Unit Files (configuration format), Systemd Timers (scheduling feature)

## References

1. Systemd documentation: https://www.freedesktop.org/software/systemd/man/systemd.service.html

#linux #systemd #service-management #devops

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**Connections:**
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**Sources:**
- From: Getting back to the EU from Google Cloud to Self-Hosted EU Infrastructure