Cluster SSH (cssh) is one of mankind’s greatest achievements. Really. Or at least, from a sysadmin point of view. It’s one of those programs that, once you know it and start using it, you wonder how were you able to survive all those dark years without it.

cssh takes a username and several IP addresses on the command line, and opens a SSH session against each of those servers on an independent xterm window. Then, you can click on any of these windows and work independently with that particular server, or go back to the cssh console and write there, and ssh will retransmit each keypress to every SSH session.

This is a very useful tool when working with server farms, clusters, etc. For example lately I’ve been doing some monitoring and maintenance tasks on a 32-server farm on a major ISP: one by one each config modification would have take hours, with cssh it is a matter of minutes. Besides, as it replicates every keypress, it even works with text editors like vi: you can edit a file on every server at the same time, navigate through it, modify it… in parallel on every server. You have to be very careful when doing this, though.