When I tried to catch ethernet traffic the program WireShark did not find any devicec. I looked in the file /usr/share/doc/wireshark/README.Debian, but could not solve the problem. Then I found this solution on http://superuser.com/questions/81233/wireshark-permission-problem-in-ubuntu
I had a similar issue with not being able to see any network interfaces when running Wireshark (tshark’s GUI cousin) as a non-root user. Nowadays, Ubuntu and Debian support file capabilities with which I was able to get Wireshark (and tshark) running as non-root.
First, create a wireshark group:
:~$ sudo groupadd wireshark
Second, add your username to the wireshark group
:~$ sudo usermod -a -G wireshark yourusername
Third, change group ownership of dumpcap to wireshark group
:~$ sudo chgrp wireshark /usr/bin/dumpcap
Fourth, set file permissions of dumpcap to 754 (rwx for user, r-x for group)
:~$ sudo chmod 754 /usr/bin/dumpcap
Fifth, enable file capabilities for dumpcap
:~$ sudo setcap 'CAP_NET_RAW+eip CAP_NET_ADMIN+eip' /usr/bin/dumpcap
You may also need to run dpkg-reconfigure for wireshark-common if you install wireshark or tshark as a package through Synaptic and enable packet capture for non-root users
:~$ sudo dpkg-reconfigure wireshark-common