mininet/mininet — pull request #250 by rlane (2013-12-14 19:22:50+00:00)
Title: kill entire process group in Node.terminate

mnexec already puts the shell into its own process group. Killing the entire
process group cleans up after any background processes the user left running.

I ran into this issue when running tcpdump in the background on a few nodes. After quitting mininet the tcpdump processes were reparented to init and kept running.