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| .\" @(#)hostname.7 8.2 (Berkeley) 12/30/93 |
| .\" $FreeBSD: src/share/man/man7/hostname.7,v 1.7 2004/07/03 18:29:23 ru Exp $ |
| .\" |
| .\" 2008-06-11, mtk, Taken from FreeBSD 6.2 and modified for Linux. |
| .\" |
| .TH HOSTNAME 7 2019-05-09 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| hostname \- hostname resolution description |
| .SH DESCRIPTION |
| Hostnames are domains, where a domain is a hierarchical, dot-separated |
| list of subdomains; for example, the machine "monet", in the "example" |
| subdomain of the "com" domain would be represented as "monet.example.com". |
| .PP |
| Each element of the hostname must be from 1 to 63 characters long and the |
| entire hostname, including the dots, can be at most 253 characters long. |
| Valid characters for hostnames are |
| .BR ASCII (7) |
| letters from |
| .I a |
| to |
| .IR z , |
| the digits from |
| .I 0 |
| to |
| .IR 9 , |
| and the hyphen (\-). |
| A hostname may not start with a hyphen. |
| .PP |
| Hostnames are often used with network client and server programs, |
| which must generally translate the name to an address for use. |
| (This task is generally performed by either |
| .BR getaddrinfo (3) |
| or the obsolete |
| .BR gethostbyname (3).) |
| .PP |
| Hostnames are resolved by the NSS framework in glibc according |
| to the |
| .B hosts |
| configuration in |
| .BR nsswitch.conf . |
| The DNS-based name resolver |
| (in the |
| .B dns |
| NSS service module) resolves them in the following fashion. |
| .PP |
| If the name consists of a single component, that is, contains no dot, |
| and if the environment variable |
| .B HOSTALIASES |
| is set to the name of a file, |
| that file is searched for any string matching the input hostname. |
| The file should consist of lines made up of two white-space separated strings, |
| the first of which is the hostname alias, |
| and the second of which is the complete hostname |
| to be substituted for that alias. |
| If a case-insensitive match is found between the hostname to be resolved |
| and the first field of a line in the file, the substituted name is looked |
| up with no further processing. |
| .PP |
| If the input name ends with a trailing dot, |
| the trailing dot is removed, |
| and the remaining name is looked up with no further processing. |
| .PP |
| If the input name does not end with a trailing dot, it is looked up |
| by searching through a list of domains until a match is found. |
| The default search list includes first the local domain, |
| then its parent domains with at least 2 name components (longest first). |
| For example, |
| in the domain cs.example.com, the name lithium.cchem will be checked first |
| as lithium.cchem.cs.example and then as lithium.cchem.example.com. |
| lithium.cchem.com will not be tried, as there is only one component |
| remaining from the local domain. |
| The search path can be changed from the default |
| by a system-wide configuration file (see |
| .BR resolver (5)). |
| .SH SEE ALSO |
| .BR getaddrinfo (3), |
| .BR gethostbyname (3), |
| .BR nsswitch.conf (5), |
| .BR resolver (5), |
| .BR mailaddr (7), |
| .BR named (8) |
| .PP |
| .UR http://www.ietf.org\:/rfc\:/rfc1123.txt |
| IETF RFC\ 1123 |
| .UE |
| .PP |
| .UR http://www.ietf.org\:/rfc\:/rfc1178.txt |
| IETF RFC\ 1178 |
| .UE |
| .\" .SH HISTORY |
| .\" Hostname appeared in |
| .\" 4.2BSD. |