error with squid: Page faults with physical i/o: 0

[vladone]

I have installed squid from ports and i try to build the cache:
#: /usr/local/sbin/squid -z
and receive:
FATAL: Could not determine fully qualified hostname.  Please set 'visible_hostname'

Squid Cache (Version 2.5.STABLE10): Terminated abnormally.
CPU Usage: 0.006 seconds = 0.006 user + 0.000 sys
Maximum Resident Size: 1720 KB
Page faults with physical i/o: 0
Abort (core dumped)

How i can resolv this?