WireGuard: Unable to modify interface: Address already in use

What it means

The ListenPort of this interface is already taken by another process or another WireGuard interface.

Why it happens

• Two configs use the same ListenPort.
• The old interface is still up (wg-quick up run twice).
• Another program listens on that UDP port.

How to fix it

1. wg show and ss -ulpn | grep <port> to find who holds it.
2. wg-quick down the old interface, or give each interface its own port.

Useful tools

Port directory

Other WireGuard errors

• Handshake for peer 1 (203.0.113.10:51820) did not complete after 5 seconds, retrying (try
• Packet has unallowed src IP (10.0.0.7) from peer 3 (198.51.100.20:43210)
• RTNETLINK answers: Operation not supported / Unable to access interface: Protocol not supp
• /usr/bin/wg-quick: line 32: resolvconf: command not found
• Key is not the correct length or format: `abc…`
• Name or service not known: `vpn.example.com:51820' / Configuration parsing error