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

       IETF RFC 1178

Linux man-pages 6.7                                2023-11-11                                        hostname(7)