I know you see it when you boot the system, but if the system's been up for a long time (we are talking Unix here, after all) you probably wouldn't want to reboot it.
The command is uname as is usually followed by a switch or two..
uname -rs
FreeBSD 5.2.1-RELEASE
and..
uname -a
FreeBSD servername.domain.net
5.2.1-RELEASE FreeBSD 5.2.1-RELEASE #0: Mon Feb 23 20:45:55 GMT 2004
root@wv1u.btc.adaptec.com:/usr/obj/usr/src/sys/GENERIC i386
For more information,
man uname..
- A.