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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)hostname.7 8.2 (Berkeley) 12/30/93 33.\" $FreeBSD$ 34.\" 35.Dd December 30, 1993 36.Dt HOSTNAME 7 37.Os 38.Sh NAME 39.Nm hostname 40.Nd host name resolution description 41.Sh DESCRIPTION 42Hostnames are domains, where a domain is a hierarchical, dot-separated 43list of subdomains; for example, the machine monet, in the Berkeley 44subdomain of the EDU subdomain of the Internet would be represented as 45.Pp 46.Dl monet.Berkeley.EDU 47.Pp 48(with no trailing dot). 49.Pp 50Hostnames are often used with network client and server programs, 51which must generally translate the name to an address for use. 52(This function is generally performed by the library routine 53.Xr gethostbyname 3 . ) 54Hostnames are resolved by the Internet name resolver in the following 55fashion. 56.Pp 57If the name consists of a single component, i.e., contains no dot, 58and if the environment variable 59.Dq Ev HOSTALIASES 60is set to the name of a file, 61that file is searched for any string matching the input hostname. 62The file should consist of lines made up of two white-space separated strings, 63the first of which is the hostname alias, 64and the second of which is the complete hostname 65to be substituted for that alias. 66If a case-insensitive match is found between the hostname to be resolved 67and the first field of a line in the file, the substituted name is looked 68up with no further processing. 69.Pp 70If the input name ends with a trailing dot, 71the trailing dot is removed, 72and the remaining name is looked up with no further processing. 73.Pp 74If the input name does not end with a trailing dot, it is looked up 75by searching through a list of domains until a match is found. 76The default search list includes first the local domain, 77then its parent domains with at least 2 name components (longest first). 78For example, 79in the domain CS.Berkeley.EDU, the name lithium.CChem will be checked first 80as lithium.CChem.CS.Berkeley.EDU and then as lithium.CChem.Berkeley.EDU. 81Lithium.CChem.EDU will not be tried, as there is only one component 82remaining from the local domain. 83The search path can be changed from the default 84by a system-wide configuration file (see 85.Xr resolver 5 ) . 86.Sh SEE ALSO 87.Xr gethostbyname 3 , 88.Xr resolver 5 , 89.Xr mailaddr 7 , 90.Xr named 8 91.Sh HISTORY 92.Nm Hostname 93appeared in 94.Bx 4.2 . 95