noble (7) hostname.7.gz

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 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  NSS  framework  in  glibc  according  to  the  hosts  configuration in
       nsswitch.conf(5).  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 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.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⟩