Open5GS Core Network: Launch and Verify

The Components of the Core Network

Before we start launching services, it's helpful to visualize what we're turning on. The Open5GS software suite implements the various functions of a mobile core network. For our 4G lab, we are interested in the components of the Evolved Packet Core (EPC).

As a Linux user, you can think of these architectural components as individual daemons or services managed by systemd. The following resource provides a clear list of the specific services we need for our 4G network.

Based on that resource, the key 4G services we need to run are:

• open5gs-hssd.service (Home Subscriber Server)
• open5gs-mmed.service (Mobility Management Entity)
• open5gs-sgwcd.service (Serving Gateway Control Plane)
• open5gs-sgwud.service (Serving Gateway User Plane)
• open5gs-pcrfd.service (Policy and Charging Rules Function)
• open5gs-smfd.service (Session Management Function, contains PGW-C)
• open5gs-upfd.service (User Plane Function, contains PGW-U)
• open5gs-webui.service (The web interface you used previously)

Launching the Open5GS Services

With the components identified, let's start them. Since these are all managed by systemd, we can use systemctl to control them.

You could start each service individually, but it's more efficient to start them all with a single command. In your terminal, run the following:

sudo systemctl start open5gs-hssd open5gs-mmed open5gs-sgwcd open5gs-sgwud open5gs-pcrfd open5gs-smfd open5gs-upfd

Note: We assume the open5gs-webui.service is already running from the last lesson. If not, you can add it to the command above or start it separately.

Verifying Operation

Launching the services is only half the task. Verifying they started correctly and are communicating is critical. A failure in one service can cause a cascade of issues. We'll use a few methods, from a quick status check to a more detailed log analysis.

Method 1: Check Service Status with systemctl

The most direct way to check if the services are running is to query systemctl. You can check them all at once using a wildcard.

sudo systemctl status 'open5gs-*'

This command will list the status of all services whose names begin with open5gs-. You should see Active: active (running) for each one. If any service has failed, this output is the first place to look for error messages.

The following video demonstrates this exact process and shows you what a healthy output looks like.

Method 2: Log File Analysis

The status check tells you if a process is running, but logs tell you what it's doing. This is where you'll find confirmation of successful initialization and inter-service communication. For a cybersecurity professional, reading logs is second nature, and here it's the key to confirming a healthy core network.

Open5GS services can be logged in two primary ways: through the journald daemon or to flat files in /var/log/open5gs/.

Using journalctl:
This is the standard systemd way to view logs. Let's look at the MME log, as it's the central orchestrator for device connections.

sudo journalctl -f -u open5gs-mmed

• The -f flag "follows" the log, showing new entries in real time.
• The -u flag filters for a specific systemd unit (service).

Tailing Log Files directly:
Alternatively, you can tail the individual log files. This can be useful for watching multiple logs at once in different terminal windows.

sudo tail -f /var/log/open5gs/mme.log

What to Look For:
The most important startup event is the MME successfully connecting to the HSS to be able to authenticate subscribers. In the MME log (viewed with either journalctl or tail), you should look for lines that indicate:

1. The MME has initialized its S1AP interface (the interface that connects to the base station).
2. The MME has successfully established a connection to the HSS.

The video you just watched also points out these key log entries.

For a deeper understanding of log interpretation and other verification techniques, the following resources are excellent.

Feel free to open multiple terminal windows to tail the logs for the HSS (hss.log), MME (mme.log), and SGW-C (sgwc.log) simultaneously. This will give you a dynamic view of the system as it operates.

Conclusion

Excellent work. You have successfully launched the Open5GS core network and, more importantly, learned how to verify that it is operating correctly. By checking service statuses and inspecting log files for key handshake messages, you've confirmed that the "brain" of your private LTE network is online and ready for action.

Key Takeaways:

• The 4G EPC is composed of several distinct services (MME, HSS, SGW, etc.) that run as systemd daemons in Open5GS.
• Verification is a crucial step after launching the services. A simple systemctl status 'open5gs-*' provides a high-level health check.
• Log analysis via journalctl or by tailing files in /var/log/open5gs/ provides the definitive proof of a healthy system.
• The most critical startup event to confirm in the logs is the MME's successful initialization and its connection to the HSS.

Preview of the Next Lesson:

Your core network is now running and is essentially waiting for a base station to connect to it. In the next lesson, you will start the srsENB base station and confirm its connection to the core network. This will establish the S1 link between the radio access network (our srsENB) and the core network (our Open5GS MME), bringing us one major step closer to connecting a device.