Purging and Reinstalling Beszel Agent (Linux)

This Knowledge Base (KB) article documents the "Nuke and Pave" method. This is the most reliable way to resolve "Invalid SSH Key" errors, service crashes, or corrupted configurations on your Ubuntu Server instances.

Scenario: Use this procedure if the Beszel Hub shows a red "Offline" dot despite the service running, or if journalctl reports failed to parse key or illegal base64 data.

Logic: This method forcefully terminates lingering processes, clears the systemd memory cache, and deletes the unprivileged user to ensure the new installation starts from a completely "zeroed" state.

Phase 1: The "Nuke" (Complete Removal)

Run this block to obliterate the existing installation. This is safe to run even if some files are already missing.

# 1. Force kill any hung agent processes
sudo killall -9 beszel-agent 2>/dev/null

# 2. Stop and disable the service unit
sudo systemctl stop beszel-agent.service 2>/dev/null
sudo systemctl disable beszel-agent.service 2>/dev/null

# 3. Delete the service configuration and binary files
sudo rm -f /etc/systemd/system/beszel-agent.service
sudo rm -rf /opt/beszel-agent

# 4. Remove the dedicated agent user
sudo userdel beszel 2>/dev/null

# 5. Flush the systemd daemon cache
sudo systemctl daemon-reload

Phase 2: The "Pave" (Clean Reinstall)

Execute the master installation command. This uses your verified Public Key to ensure an immediate handshake with the CasaOS Hub.

curl -sL https://get.beszel.dev -o /tmp/install-agent.sh && \
chmod +x /tmp/install-agent.sh && \
sudo /tmp/install-agent.sh -p 45876 -k "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICJ7lFlWxcv1b25gymPNRAvp0ptAJChTuNYvmnomZpFW"

Phase 3: Post-Flight Verification

After the script reports success, verify that the service is active and that the connection is established.

1. Check Service Heartbeat

sudo systemctl status beszel-agent.service

Target: Active: active (running)

2. Verify Hub Communication

sudo journalctl -u beszel-agent.service -n 20 --no-pager

• Target: You should see INFO Starting SSH server addr=:45876.
• Target: You should not see any WARN messages regarding "Invalid SSH key."

Admin Tips for the Micro PC Environment

• Hostname Resolution: If you see sudo: unable to resolve host, ensure your /etc/hosts file matches your hostname:
  echo "127.0.1.1 $(hostname)" | sudo tee -a /etc/hosts 
• NVMe Lifespan: By using the "Nuke and Pave" method only when troubleshooting, you avoid unnecessary write cycles on your 512GB NVMe SSD. The agent itself runs primarily in RAM (approx. 6-10MB).
• Remote Management: If a server becomes unreachable during this process, use your JetKVM to access the tty console directly and verify the network interface with ip a.

Next Step: Your Linux recovery documentation is complete. Shall we proceed with the Windows 11 agent installation using the NSSM service manager method?