It seems PACKET_MMAP was added to the main libpcap distribution in January 2008: http://github.com/mcr/libpcap/commit/92c5d33d7a89c624e90b55f95bb7fbc49ec06c5f Are you sure the Debian package doesn't already support mmap? (I have no evidence that it does; in fact, I'm a bit unsure how to check whether tcpdump is using mmap or not)