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       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 NSS framework in glibc according to the hosts  configuration
       in  nsswitch.conf.   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, 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), nsswitch.conf(5), resolver(5), mailaddr(7), named(8)

       IETF RFC 1123 ⟨⟩

       IETF RFC 1178 ⟨


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