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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.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)).
SEE ALSO
       getaddrinfo(3), gethostbyname(3), 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 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
       https://www.kernel.org/doc/man-pages/.
Linux                             2017-05-03                       HOSTNAME(7)