Analyzing a Linux game server's logs with journalctl

When a Linux game server restarts, refuses a connection or stops launching a service, the logs let you replace assumptions with verifiable facts. On a VPS server, a private server or a dedicated server running Ubuntu or Debian, journalctl reads the messages centralized by systemd and journald. This method helps configure and administer a virtual server intended to host a game, on a cloud infrastructure or a physical machine, without confusing an application failure with a virtualization problem.

Before starting the diagnosis

Connect over SSH with an account allowed to read the logs. An administrator can use root or sudo, depending on the operating system configuration. Note the exact time of the problem, the game name, the service name and the action that preceded the incident. This timeline helps filter the events.

Check the VPS's basic resources: processor, CPU, RAM, storage space and SSD status. Memory, storage or bandwidth saturation can accompany a restart. If your architecture uses a database, a web server, a proxy or a control panel, also note the service involved. A log is only useful if you consult the right unit.

The examples are read commands. Replace mon-jeu.service with the real name of your systemd unit. To find the active units, start with systemctl list-units --type=service. Do not copy a service name found in a tutorial that concerns a different installation.

Viewing the service status

Start with the unit's current status:

systemctl status mon-jeu.service --no-pager

This command displays the status known to systemd and the last associated lines. If the service has failed, note the code or the reason, then consult the logs. The status does not replace the logs: the important message may be a few seconds before the last event.

Filtering logs by service

To display the messages attached to a specific unit:

journalctl -u mon-jeu.service --no-pager

To limit the output to the latest events:

journalctl -u mon-jeu.service -n 100 --no-pager

With -f, the command follows new messages. This is useful for reproducing a startup or a reconnection in a second SSH window:

journalctl -u mon-jeu.service -f

Stop this follow with Ctrl+C. Watching a log does not repair the server: keep the message that describes the failure before changing the configuration.

Limiting the period under review

If the incident happened at a known time, use a time window:

journalctl -u mon-jeu.service --since "2026-09-17 10:00" --until "2026-09-17 10:15" --no-pager

For the current boot:

journalctl -u mon-jeu.service -b --no-pager

This approach avoids attributing an old, already-resolved error to the current incident. It is suited to game server hosting where several services can write at the same time.

Reading the priority levels

To examine the warnings and errors associated with the service:

journalctl -u mon-jeu.service -p warning..err --since today --no-pager

A warning is not automatically the cause of an outage. Compare its time with the moment the game server stopped responding. A repeated startup failure is generally more useful than an isolated line.

Spotting the useful message

Look for the impossible actions: file not found, permission denied, port already in use, invalid configuration, missing dependency or requested shutdown. The chronological order can show a first error, followed by several consequences.

journalctl -u mon-jeu.service --since "2026-09-17 10:00" --until "2026-09-17 10:15" --no-pager > diagnostic-serveur.txt

Before sharing this file, remove IP addresses, credentials, private paths and tokens. Never publish an SSH key, a password, an application secret or a database connection string.

Linking the game service to the system

If the service seems to start but the game remains unreachable, compare its logs with the system events of the same period. A unit can be active while the child process has stopped, a port is taken or a resource is missing.

journalctl -b --since "10 minutes ago" --no-pager

Keep the exact unit name, the time and the relevant lines. You can then check the process, the IP address, the port, the DNS and the firewall. If you use a panel, a proxy or several virtual machines, compare the time of the displayed action with that of the log.

Not confusing logs and connectivity

A systemd log explains the start and stop of the service, but does not prove that the port is reachable from the Internet. If no application error appears, check the public IP address, the declared port, the local firewall and the provider's network rules. This separation avoids changing the game server when the process is already working.

A CPU, RAM or disk alert must be confirmed by an appropriate measurement. A large log file can fill a VPS's storage space. Memory pressure can cause a process to stop. In that case, look for the system event corresponding to the same period before concluding. A monitoring tool can help compare the metrics with the time of the message.

Preserving configuration and backups

Before a significant change, back up the configuration and verify that the backup can be restored. A high-availability backup does not replace a restore test, but it limits the risk during maintenance. Also keep a copy of the diagnosis, without secrets, to compare the state before and after the fix.

If the virtual server hosts several applications, isolate the services involved. Do not restart a web server, a database or another game just because a different unit is in error. Precise log reading reduces hosting interruptions.

After the diagnosis

Do not delete logs to make an error disappear. Fix a single cause at a time, restart the service according to your procedure, then check the new startup with systemctl status and journalctl -u. Note the command and the result so you can roll back.

If the log indicates a permission, a configuration file or a missing dependency, check the path and the service user before changing the permissions. If the message concerns a port, first identify the process using it. If no line matches the time of the incident, gradually widen the period and check the unit.

To deepen your preparation, also check out the first security settings for a dedicated server, installing Docker on a VPS, diagnosing an unreachable VPS, dedicated server backups and the criteria to check before renting a dedicated server.