1.\" $OpenBSD: hostname.7,v 1.5 2000/03/04 22:19:33 aaron 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. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)hostname.7 8.2 (Berkeley) 12/30/93 36.\" 37.Dd December 30, 1993 38.Dt HOSTNAME 7 39.Os 40.Sh NAME 41.Nm hostname 42.Nd host name resolution description 43.Sh DESCRIPTION 44Hostnames are domains, where a domain is a hierarchical, dot-separated 45list of subdomains; for example, the machine monet, in the Berkeley 46subdomain of the EDU subdomain of the Internet would be represented as 47.Pp 48.Dl monet.Berkeley.EDU 49.Pp 50(with no trailing dot). 51.Pp 52Hostnames are often used with network client and server programs, 53which must generally translate the name to an address for use. 54(This function is generally performed by the library routine 55.Xr gethostbyname 3 . ) 56Hostnames are resolved by the Internet name resolver in the following 57fashion. 58.Pp 59If the name consists of a single component, i.e. contains no dot, 60and if the environment variable 61.Ev HOSTALIASES 62is set to the name of a file, 63that file is searched for any string matching the input hostname. 64The file should consist of lines made up of two whitespace separated strings, 65the first of which is the hostname alias, 66and the second of which is the complete hostname 67to be substituted for that alias. 68If a case-insensitive match is found between the hostname to be resolved 69and the first field of a line in the file, the substituted name is looked 70up with no further processing. 71.Pp 72If the input name ends with a trailing dot, 73the trailing dot is removed, 74and the remaining name is looked up with no further processing. 75.Pp 76If the input name does not end with a trailing dot, it is looked up 77by searching through a list of domains until a match is found. 78The default search list includes first the local domain, 79then its parent domains with at least 2 name components (longest first). 80For example, 81in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first 82as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. 83Lithium.CChem.EDU will not be tried, as there is only one component 84remaining from the local domain. 85The search path can be changed from the default 86by a system-wide configuration file (see 87.Xr resolv.conf 5 ) . 88.Sh SEE ALSO 89.Xr gethostbyname 3 , 90.Xr resolv.conf 5 , 91.Xr mailaddr 7 , 92.Xr named 8 93.Sh HISTORY 94A 95.Nm 96manual page appeared in 97.Bx 4.2 . 98