Tcpdump

tcpdump is a command-line network monitoring and data acquisition tool. It is capable of sniffing packets and "dumping" information.

Emerge
Install tcpdump:

Configuration
In order for normal users to run tcpdump they need to be added to the tcpdump group. Do this by using the usermod command where  is user's username:

Invocation
If a standard user has been added to the  group the following command should be executable without needing root permissions:

External resources

 * http://www.tcpdump.org/manpages/pcap.3pcap.html - The tcpdump man page hosted on the web.