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 charac‐
       ters 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 per‐
       formed 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.  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  in‐
       cludes  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)).

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⟩

Linux                                                                          2019-05-09                                                                    HOSTNAME(7)