Networking, services and logs on Linux

A Linux server exists to make services reachable over the network. This block closes the loop of the fundamentals: you learn to read the network configuration, to check the state of services with systemd, to read the logs with journalctl, and to diagnose a problem when something does not work.

Why this block exists

Handling files and managing packages is not enough. As soon as a server is on a network, you must answer three questions:

• is it reachable?: network configuration, DNS, routes;
• are its services running?: systemd, units, automatic start;
• what happened when it broke?: logs, troubleshooting, diagnosis.

This block covers these three pillars and gives you a systematic troubleshooting method.

The recommended path

The four guides of the module go from connectivity to diagnosis: you check that the machine is reachable, then that its services run, and you read the logs when one of the two fails.

The logical order

The network first (no network, no service), then systemd services, then the logs to diagnose. The troubleshooting guide comes last because it builds on all the others.

1. Understand and test the network

The networking basics guide sets out the concepts behind a server's connectivity: IP addresses, interfaces, routes and DNS. The one to test connectivity puts them to the test with ping, ss, curl and traceroute, to find at which layer a communication fails.

2. Check the services

In this block, systemctl status is enough: it tells you whether a service is running, since when, and with which last log lines. Full management, starting, stopping, enabling at boot, units and dependencies, is taught in the Operate part with the systemd services guide, which is not part of this module but extends it directly.

3. Read the logs and diagnose

The journalctl guide teaches you to read the system logs, filter them by service or by date and follow them live. The Linux troubleshooting guide brings it all together into a systematic method: service, logs, network, then resources.

Key points

• ip a shows the network interfaces, ip r the routes: remember these two commands.
• systemctl status <service> is your first reflex when a service does not respond.
• journalctl -u <service> --since "10 min ago" filters the service's logs over the last 10 minutes.
• Efficient troubleshooting follows an order: service → logs → network → resources (disk, memory).
• This block closes the fundamentals: you have the basics to administer a Linux server.

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