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Managing systemd Services: Install, Start, Stop, Pause, and Resume

systemd is a powerful system and service manager for Linux, widely used across major distributions like Ubuntu, Fedora, and Arch Linux. It provides a unified way to manage system processes, services, and resources. This guide covers the essentials of installing, starting, stopping, pausing, and resuming services with systemd.

1. Installing Systemd Services

In most Linux distributions, systemd is pre-installed. However, if you're creating a new service or installing software that includes a systemd service, you may need to manually configure or install the service file.

Creating a Systemd Service File

To create a custom service file for systemd, follow these steps:

  1. Create a new service file in the /etc/systemd/system/ directory: 
    
sudo nano /etc/systemd/system/myservice.service
  2. Define the service by adding the following basic structure: 
    
[Unit]
Description=My Custom Service
After=network.target

[Service]
ExecStart=/path/to/executable
Restart=on-failure

[Install]
WantedBy=multi-user.target
    • Description: A short description of the service.
    • After: Specifies dependencies, so the service starts after these dependencies are loaded.
    • ExecStart: The command to execute when the service starts.
    • Restart: Defines the service restart behavior (e.g., restart on failure).
    • WantedBy: Defines the target for the service (multi-user mode in this case).
  3. Reload systemd to recognize the new service file: 
    
sudo systemctl daemon-reload
  4. Enable the service to start automatically at boot: 
    
sudo systemctl enable myservice

2. Starting and Stopping a Systemd Service

Once a service is installed and configured, you can start or stop it with systemctl.

Start a Service

To start a systemd service: 


sudo systemctl start myservice
  • Replace myservice with the actual service name.
  • This command immediately runs the service specified in the ExecStart directive.

Stop a Service

To stop a systemd service: 


sudo systemctl stop myservice

This halts the service without affecting its configuration or boot behavior.

Enable and Disable a Service

  • Enable the service to start on boot: 
    
sudo systemctl enable myservice
  • Disable the service to prevent it from starting on boot: 
    
sudo systemctl disable myservice

3. Pausing and Resuming a Systemd Service

systemd does not directly support pausing services, but you can simulate pausing by suspending the main process. Here's how:

Pausing a Service Using SIGSTOP

  1. First, identify the main process ID (PID) for the service: 
    
sudo systemctl show -p MainPID --value myservice
  2. Send the SIGSTOP signal to pause the process: 
    
sudo kill -SIGSTOP

    Replace <PID> with the process ID obtained from the previous command. This halts the process without stopping the service entirely.

Resuming a Paused Service Using SIGCONT

To resume the paused service, send the SIGCONT signal: 


sudo kill -SIGCONT

This resumes the process from where it was paused.

4. Checking the Status of a Service

To view the current status of a service, use: 


sudo systemctl status myservice

This command provides details, including whether the service is active, inactive, failed, or paused (if manually paused with SIGSTOP).

5. Restarting a Systemd Service

You may want to restart a service to apply new configurations or to refresh its state. To restart a service: 


sudo systemctl restart myservice

This command stops and then starts the service in one step.

6. Additional Systemd Commands

Here are some additional systemd commands for managing services:

  • Reload a Service Configuration: Reloads the configuration without fully restarting: 
    
sudo systemctl reload myservice
  • List All Services: 
    
systemctl list-units --type=service
  • View Logs for a Service:
    systemd is integrated with the journalctl logging system. To view logs for a service, use: 
    
sudo journalctl -u myservice

Summary

With systemd, managing services becomes more standardized and flexible. This guide covered:

  • Installing and configuring systemd services
  • Starting, stopping, enabling, and disabling services
  • Simulating pause and resume with SIGSTOP and SIGCONT signals
  • Checking status and viewing logs

Understanding systemd allows for efficient control of processes on Linux systems, whether for managing background services or building a reliable server environment.