Xauth error when using ssh from Mac to Linux

Symptoms

The command ssh -X or ssh -Y to a remote Linux machine produces an error similar to one of these:

• Warning: untrusted X11 forwarding setup failed: xauth key data not generated
• Warning: No xauth data; using fake authentication data for X11 forwarding

Environment

• macOS
• XQuartz

Cause

XQuartz is old and needs to be updated.

Resolution

Update XQuartz to the latest available version.