of pty/tty based (since they have several annoying problems
associated). Note that permission is granted via the use of an "acl"
file; /dev/tip/machine.acl, which must be set to the group of the
project the node is in, so the user can read out the process id number
and the random bits that are used by capture to grant permission to
use (tip sends the random bits across first thing). This handshake is
due to change to a request/challenge scheme as described by Dave in
email to the testbed list.