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.\" $FreeBSD$ 30.\" 31.Dd December 25, 2013 32.Dt HOSTNAME 7 33.Os 34.Sh NAME 35.Nm hostname 36.Nd host name resolution description 37.Sh DESCRIPTION 38Hostnames are domains, where a domain is a hierarchical, dot-separated 39list of subdomains; for example, the machine monet, in the Berkeley 40subdomain of the EDU subdomain of the Internet would be represented as 41.Pp 42.Dl monet.Berkeley.EDU 43.Pp 44(with no trailing dot). 45.Pp 46Hostnames are often used with network client and server programs, 47which must generally translate the name to an address for use. 48(This function is generally performed by the library routine 49.Xr gethostbyname 3 . ) 50Hostnames are resolved by the Internet name resolver in the following 51fashion. 52.Pp 53If the name consists of a single component, i.e., contains no dot, 54and if the environment variable 55.Dq Ev HOSTALIASES 56is set to the name of a file, 57that file is searched for any string matching the input hostname. 58The file should consist of lines made up of two white-space separated strings, 59the first of which is the hostname alias, 60and the second of which is the complete hostname 61to be substituted for that alias. 62If a case-insensitive match is found between the hostname to be resolved 63and the first field of a line in the file, the substituted name is looked 64up with no further processing. 65.Pp 66If the input name ends with a trailing dot, 67the trailing dot is removed, 68and the remaining name is looked up with no further processing. 69.Pp 70If the input name does not end with a trailing dot, it is looked up 71by searching through a list of domains until a match is found. 72The default search list includes first the local domain, 73then its parent domains with at least 2 name components (longest first). 74For example, 75in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first 76as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. 77Lithium.CChem.EDU will not be tried, as there is only one component 78remaining from the local domain. 79The search path can be changed from the default 80by a system-wide configuration file (see 81.Xr resolver 5 ) . 82.Sh SEE ALSO 83.Xr gethostbyname 3 , 84.Xr resolver 5 85.Sh HISTORY 86.Nm Hostname 87appeared in 88.Bx 4.2 . 89