1HOSTNAME(7)                Linux Programmer's Manual               HOSTNAME(7)


6       hostname - hostname resolution description


9       Hostnames  are domains, where a domain is a hierarchical, dot-separated
10       list of subdomains; for example, the machine "monet", in the  "example"
11       subdomain  of  the  "com"  domain  would be represented as "monet.exam‐
12       ple.com".
14       Each element of the hostname must be from 1 to 63 characters  long  and
15       the  entire hostname, including the dots, can be at most 253 characters
16       long.  Valid characters for hostnames are ASCII(7) letters from a to z,
17       the  digits  from 0 to 9, and the hyphen (-).  A hostname may not start
18       with a hyphen.
20       Hostnames are often used with network client and server programs, which
21       must generally translate the name to an address for use.  (This task is
22       generally performed by either getaddrinfo(3) or the obsolete gethostby‐
23       name(3).)   Hostnames are resolved by the Internet name resolver in the
24       following fashion.
26       If the name consists of a single component, that is, contains  no  dot,
27       and  if  the  environment  variable HOSTALIASES is set to the name of a
28       file, that file is searched for any string matching the input hostname.
29       The  file  should consist of lines made up of two white-space separated
30       strings, the first of which is the hostname alias, and  the  second  of
31       which  is the complete hostname to be substituted for that alias.  If a
32       case-insensitive match is found between the hostname to be resolved and
33       the  first  field of a line in the file, the substituted name is looked
34       up with no further processing.
36       If the input name ends  with  a  trailing  dot,  the  trailing  dot  is
37       removed,  and  the remaining name is looked up with no further process‐
38       ing.
40       If the input name does not end with a trailing dot, it is looked up  by
41       searching  through  a  list  of  domains  until  a match is found.  The
42       default search list includes first the local domain,  then  its  parent
43       domains  with at least 2 name components (longest first).  For example,
44       in the domain cs.example.com, the name lithium.cchem  will  be  checked
45       first  as  lithium.cchem.cs.example  and  then  as  lithium.cchem.exam‐
46       ple.com.  lithium.cchem.com will not be tried, as  there  is  only  one
47       component  remaining  from  the  local  domain.  The search path can be
48       changed from the default  by  a  system-wide  configuration  file  (see
49       resolver(5)).


52       getaddrinfo(3), gethostbyname(3), resolver(5), mailaddr(7), named(8)
54       IETF RFC 1123 ⟨http://www.ietf.org/rfc/rfc1123.txt
56       IETF RFC 1178 ⟨http://www.ietf.org/rfc/rfc1178.txt


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66Linux                             2017-05-03                       HOSTNAME(7)