Provided by: manpages_4.15-1_all bug


       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 "".

       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  Internet
       name resolver 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, 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


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

       IETF RFC 1123 ⟨⟩

       IETF RFC 1178 ⟨


       This  page  is  part of release 4.15 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