A "public" machine is a machine that can be logged into by anyone with a CS account; the name linux.cs.utexas.edu is always aliased to a public Linux machine. You can use the command cshosts to find out more information about other machines on the CS network; type cshosts help or man cshosts for more information about how to use it. Alternatively, you can visit the public host status page for a list of public hosts and their current status.