1.\" Copyright (c) 1987, 1990, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)hostname.7 8.2 (Berkeley) 12/30/93 29.\" $FreeBSD: src/share/man/man7/hostname.7,v 1.5.2.1 2001/08/17 13:08:49 ru Exp $ 30.\" $DragonFly: src/share/man/man7/hostname.7,v 1.2 2003/06/17 04:37:00 dillon Exp $ 31.\" 32.Dd December 30, 1993 33.Dt HOSTNAME 7 34.Os 35.Sh NAME 36.Nm hostname 37.Nd host name resolution description 38.Sh DESCRIPTION 39Hostnames are domains, where a domain is a hierarchical, dot-separated 40list of subdomains; for example, the machine monet, in the Berkeley 41subdomain of the EDU subdomain of the Internet would be represented as 42.Pp 43.Dl monet.Berkeley.EDU 44.Pp 45(with no trailing dot). 46.Pp 47Hostnames are often used with network client and server programs, 48which must generally translate the name to an address for use. 49(This function is generally performed by the library routine 50.Xr gethostbyname 3 . ) 51Hostnames are resolved by the Internet name resolver in the following 52fashion. 53.Pp 54If the name consists of a single component, i.e. contains no dot, 55and if the environment variable 56.Dq Ev HOSTALIASES 57is set to the name of a file, 58that file is searched for any string matching the input hostname. 59The file should consist of lines made up of two white-space separated strings, 60the first of which is the hostname alias, 61and the second of which is the complete hostname 62to be substituted for that alias. 63If a case-insensitive match is found between the hostname to be resolved 64and the first field of a line in the file, the substituted name is looked 65up with no further processing. 66.Pp 67If the input name ends with a trailing dot, 68the trailing dot is removed, 69and the remaining name is looked up with no further processing. 70.Pp 71If the input name does not end with a trailing dot, it is looked up 72by searching through a list of domains until a match is found. 73The default search list includes first the local domain, 74then its parent domains with at least 2 name components (longest first). 75For example, 76in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first 77as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. 78Lithium.CChem.EDU will not be tried, as there is only one component 79remaining from the local domain. 80The search path can be changed from the default 81by a system-wide configuration file (see 82.Xr resolver 5 ) . 83.Sh SEE ALSO 84.Xr gethostbyname 3 , 85.Xr resolver 5 , 86.Xr mailaddr 7 , 87.Xr named 8 88.Sh HISTORY 89.Nm Hostname 90appeared in 91.Bx 4.2 . 92