GENWiki

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.exam-
     ple.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 gethostby-
     name(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 process-
     ing.

     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.exam-
     ple.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)).