Is possible to "sniff" a socket? Socat doesn't work

This is the situation: I have two VM (virtual machines) via kvm-qemu connected via virtual-serial (a socket). I created the two vm's with this serial configuration: serial1 (slackware, uses port1 which is ttyS1 or com2) serial2 (unixware use port 0, which is ttyS0 or COM1) The serial works ssh unixware2 cu Slackware1 Connected slackware1 login: I want to sniff the traffic! Searching on net i found this I did that... sudo socat TCP-LISTEN:6004,reuseaddr,fork UNIX-CONNECT:/tmp/ppp.sock and sudo tcpdump -i any -f 'tcp port 6004' -vv -xX tcpdump: data link type LINUX_SLL2 tcpdump: listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes ^C 0 packets captured 0 packets received by filter 0 packets dropped by kernel as you can see 0 packet is captured. I've also tried -i lo but no success. Of course I have made some operations (using uux, cu, etc..).