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NAME | DESCRIPTION | SEE ALSO | COLOPHON |
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hostname(7) Miscellaneous Information Manual hostname(7)
hostname - hostname resolution 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".
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 ASCII(7)
letters from a to z, the digits from 0 to 9, and the hyphen (-).
A hostname may not start with a hyphen.
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 getaddrinfo(3) or the
obsolete gethostbyname(3).)
Hostnames are resolved by the NSS framework in glibc according to
the hosts configuration in nsswitch.conf(5). The DNS-based name
resolver (in the dns NSS service module) resolves them in the
following fashion.
If the name consists of a single component, that is, contains no
dot, and if the environment variable 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.
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.
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 resolver(5)).
getaddrinfo(3), gethostbyname(3), nsswitch.conf(5), resolver(5),
mailaddr(7), named(8)
IETF RFC 1123 ⟨http://www.ietf.org/rfc/rfc1123.txt⟩
IETF RFC 1178 ⟨http://www.ietf.org/rfc/rfc1178.txt⟩
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 hostname(7)
Pages that refer to this page: getaddrinfo(3), getaddrinfo_a(3), gethostbyname(3), getnameinfo(3), resolver(3), host.conf(5), hostname(5), hosts(5), resolv.conf(5), sm-notify(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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