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



NAME
       hostname - hostname resolution description

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 trans‐
       late  the  name  to  an  address for use.  (This task is generally performed by either getad‐‐
       drinfo(3) or the obsolete gethostbyname(3).)

       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 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 be‐
       tween  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 do‐
       main,  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)).

SEE ALSO
       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⟩

COLOPHON
       This  page  is  part  of  release  5.10 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 https://www.kernel.org/doc/man-pages/.



Linux                                        2019-05-09                                  HOSTNAME(7)