hostname(7) — Linux manual page


HOSTNAME(7)               Linux Programmer's Manual              HOSTNAME(7)

NAME         top

       hostname - hostname resolution description

DESCRIPTION         top

       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

       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

       Hostnames are resolved by the NSS framework in glibc according to the
       hosts configuration in nsswitch.conf.  The DNS-based name resolver
       (in the dns NSS service module) resolves them in the following

       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

       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, the name lithium.cchem will be
       checked first as lithium.cchem.cs.example and then as 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)).

SEE ALSO         top

       getaddrinfo(3), gethostbyname(3), nsswitch.conf(5), resolver(5),
       mailaddr(7), named(8)

       IETF RFC 1123 ⟨⟩

       IETF RFC 1178 ⟨

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2019-05-09                      HOSTNAME(7)

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