How to fix channel_setup_fwd_listener: cannot listen to port: port in SSH

First, verify if another process is holding the port:

lsof -i :8080
# or
netstat -tulpn | grep 8080

Replace 8080 with your actual port number. If another process is using it, either stop that process or choose a different port for your SSH forwarding.

Ensure you're using a port number higher than 1024. Ports below 1024 require root privileges:

# Wrong (if not root):
ssh -L 80:localhost:8080 [email protected]

# Correct:
ssh -L 8080:localhost:8080 [email protected]

If you need to forward privileged ports, either run SSH with sudo or use setcap to grant capabilities to your SSH client.

If you recently disconnected an SSH session, it may still hold the port. Kill hanging SSH processes:

pkill -f 'ssh.*-L.*8080'
# or forcefully
pkill -9 ssh

Wait a few seconds for the port to be fully released before reconnecting.

Check ~/.ssh/config for conflicting LocalForward or RemoteForward directives:

cat ~/.ssh/config

If you have duplicate forwarding rules for the same port, remove or comment out the conflicting ones:

Host myhost
  # Remove duplicate LocalForward lines
  LocalForward 8080 localhost:8080

If the above steps don't work, switch to a different port in the ephemeral range (40000-60000):

ssh -L 54321:destination.com:8080 [email protected]

This is often the quickest workaround while investigating the root cause.

If you're on a system with SELinux enabled, it might be blocking the port binding:

semanage port -l | grep ssh

For firewall rules, check:

sudo iptables -L -n
# or on systems with firewalld:
sudo firewall-cmd --list-ports

Add your port to SELinux or firewall if needed.