How to Control Systemd Services on Remote Linux Server?

As Linux users and administrators, we are responsible for managing services on remote Linux servers, which could include web servers like Apache or Nginx, or database servers like MySQL or PostgreSQL. To effectively manage these services, we need to have a strong understanding of the underlying system and service manager for Linux systemd.

Systemd is a robust and feature-rich system and service manager designed for Linux-based operating systems. It takes care of managing the initialization and termination of services, tracks system processes, and oversees system resources. It is widely adopted as the default system and service manager in many modern Linux distributions, such as Ubuntu, Fedora, CentOS, and Debian.

Controlling systemd services on a remote Linux server is critical for system administration. This involves tasks such as starting, stopping, restarting, enabling, disabling, and monitoring system services. While there are various methods for managing systemd services, using commands like systemctl, journalctl, and others is the most efficient and reliable way.

Step 1: Connect to the Remote Server

To connect to the remote server using SSH, open a terminal on your local machine and type the following command, replacing "username" with your own username and "remote.server.com" with the hostname or IP address of the remote server

ssh username@remote.server.com

Output may look like this

The authenticity of host 'remote.server.com (192.168.1.1)' can't be established.
RSA key fingerprint is 11:22:33:44:55:66:77:88:99:AA:BB:CC:DD:EE:FF:00.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'remote.server.com,192.168.1.1' (RSA) to the list of known hosts.
username@remote.server.com's password:

Upon successful authentication with the correct password, you will gain access to the remote server and be presented with the command terminal prompt for that particular server.

Step 2: Check the Status of a Service

Once you establish a connection with the remote server, it's essential to check the status of any service using the systemctl status command. To know the status of any service, use this command

sudo systemctl status apache2

The command sudo systemctl status apache2 will provide detailed information about the current status of the Apache service.

apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2023-03-15 14:30:00 UTC; 5min ago
   Main PID: 12345 (apache2)
      Tasks: 55 (limit: 2288)
     Memory: 67.0M
     CGroup: /system.slice/apache2.service
             ??12345 /usr/sbin/apache2 -k start
             ??12346 /usr/sbin/apache2 -k start
             ??12347 /usr/sbin/apache2 -k start
Mar 15 14:30:00 example.com systemd[1]: Started The Apache HTTP Server.

Step 3: Start a Service

To start a specific service, replace "service_name" with the actual name of the service. For example, to initiate the Apache web server on a remote server, use this command

sudo systemctl start apache2

After executing the command, you'll be prompted for your password

[sudo] password for username:

If the password is correct, the service will start successfully. No output typically means the command executed without errors.

Step 4: Stop a Service

If a service is running and you need to stop it, you can use the systemctl stop command. The syntax is as follows

sudo systemctl stop apache2

Output may look like this

[sudo] password for user:

After entering the password, the service will stop. Like the start command, no additional output usually indicates successful execution.

Step 5: Restart a Service

If you've made changes to a service configuration and need to restart it for those changes to take effect, use the systemctl restart command

sudo systemctl restart apache2

The terminal will request the user's password when using the sudo command

[sudo] password for user:

This command stops and then starts the service, ensuring that any configuration changes are applied.

Step 6: Enable a Service

If you want a service to start automatically when the system boots up, use the systemctl enable command

sudo systemctl enable apache2

If the service is not yet enabled, the output may look like this

Created symlink /etc/systemd/system/multi-user.target.wants/apache2.service ? /lib/systemd/system/apache2.service.

If the service is already enabled, you may see a message indicating synchronization with existing configurations. The systemctl enable command ensures that the service will start automatically during system boot.

Step 7: Disable a Service

To prevent a service from starting automatically at boot time, use the systemctl disable command

sudo systemctl disable apache2

This command removes the symbolic links that enable automatic startup, effectively disabling the service from starting at boot.

Step 8: Check Service Logs

If a service is not working properly or you're experiencing issues with it, use the journalctl command to check its logs

sudo journalctl -u apache2

Output for the journalctl command

-- Logs begin at Mon 2023-03-13 00:00:00 UTC, end at Mon 2023-03-13 23:59:59 UTC. --
Mar 13 08:30:01 server systemd[1]: Starting The Apache HTTP Server...
Mar 13 08:30:01 server apachectl[12345]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message
Mar 13 08:30:01 server systemd[1]: Started The Apache HTTP Server.
Mar 13 08:30:01 server systemd[1]: apache2.service: Main process exited, code=exited, status=0/SUCCESS
Mar 13 08:30:01 server systemd[1]: apache2.service: Succeeded.

You can also use additional flags like -f to follow logs in real-time or --since to view logs from a specific time period.

Common Systemctl Commands Summary

Step 9: Exit the Remote Server

Once you've completed your tasks on the remote server, you can exit the SSH session by typing the following command

exit

Here's an example of the terminal output

me@local-machine:~$ ssh remote-server
Welcome to remote-server!
me@remote-server:~$ ls
file1.txt  file2.txt  file3.txt
me@remote-server:~$ exit
logout
Connection to remote-server closed.
me@local-machine:~$

This will close the SSH connection and return you to your local machine's command prompt.

Conclusion

We have learned how to manage systemd services on a remote Linux server using essential commands like systemctl status, systemctl start, systemctl stop, systemctl restart, systemctl enable, and systemctl disable. These commands allow you to inspect service status, control service states, and manage automatic startup behavior. Mastering systemd service management on remote Linux servers is an essential skill for effective system administration and ensuring reliable service operation.