1.\" $OpenBSD: hostname.7,v 1.8 2007/05/31 19:19:58 jmc Exp $ 2.\" $NetBSD: hostname.7,v 1.4 1994/11/30 19:07:14 jtc Exp $ 3.\" 4.\" Copyright (c) 1987, 1990, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)hostname.7 8.2 (Berkeley) 12/30/93 32.\" 33.Dd $Mdocdate: May 31 2007 $ 34.Dt HOSTNAME 7 35.Os 36.Sh NAME 37.Nm hostname 38.Nd host name resolution description 39.Sh DESCRIPTION 40Hostnames are domains, where a domain is a hierarchical, dot-separated 41list of subdomains; for example, the machine monet, in the Berkeley 42subdomain of the EDU subdomain of the Internet would be represented as 43.Pp 44.Dl monet.Berkeley.EDU 45.Pp 46(with no trailing dot). 47.Pp 48Hostnames are often used with network client and server programs, 49which must generally translate the name to an address for use. 50(This function is generally performed by the library routine 51.Xr gethostbyname 3 . ) 52Hostnames are resolved by the Internet name resolver in the following 53fashion. 54.Pp 55If the name consists of a single component, i.e., contains no dot, 56and if the environment variable 57.Ev HOSTALIASES 58is set to the name of a file, 59that file is searched for any string matching the input hostname. 60The file should consist of lines made up of two whitespace separated strings, 61the first of which is the hostname alias, 62and the second of which is the complete hostname 63to be substituted for that alias. 64If a case-insensitive match is found between the hostname to be resolved 65and the first field of a line in the file, the substituted name is looked 66up with no further processing. 67.Pp 68If the input name ends with a trailing dot, 69the trailing dot is removed, 70and the remaining name is looked up with no further processing. 71.Pp 72If the input name does not end with a trailing dot, it is looked up 73by searching through a list of domains until a match is found. 74The default search list includes first the local domain, 75then its parent domains with at least 2 name components (longest first). 76For example, 77in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first 78as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. 79Lithium.CChem.EDU will not be tried, as there is only one component 80remaining from the local domain. 81The search path can be changed from the default 82by a system-wide configuration file (see 83.Xr resolv.conf 5 ) . 84.Sh SEE ALSO 85.Xr gethostbyname 3 , 86.Xr resolv.conf 5 , 87.Xr mailaddr 7 , 88.Xr named 8 89.Sh HISTORY 90A 91.Nm 92manual page appeared in 93.Bx 4.2 . 94