domainname(1)

NAME
     domainname - set or display name of current NIS domain

SYNOPSIS
     domainname [ name-of-domain ]

DESCRIPTION
     Without an argument, domainname displays the name of the current network
     information service (NIS) domain, which typically encompasses a group of
     hosts under the same administration.  As such, the name of an NIS domain
     is typically a valid Internet domain name in order to be consistent with
     the domain name used by the BIND name server, named(1M).

     Only the super-user can set the domain name by giving an argument; this
     is performed by the system startup procedure using the contents of
     /var/yp/ypdomain.

     Currently, the network information service uses domains only to refer
     collectively to a group of hosts.

SEE ALSO
     ypinit(1M)