Hmmm ... there must be an other error
netstat -tupan | grep 6001
tcp 0 0 0.0.0.0:6001 0.0.0.0:* LISTEN 28843/X
tcp 0 0 :::6001 :::* LISTEN 28843/X
strange ... detected by trying to use socat with
socat TCP-LISTEN:6001,fork,reuseaddr unix-connect:/tmp/.X11-unix/X1
2016/03/07 12:49:11 socat[29011] E bind(5, {AF=2 0.0.0.0:6001}, 16): Address
already in use