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

6       hostname - hostname resolution description
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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".
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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.
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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).)
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25       Hostnames  are  resolved by the NSS framework in glibc according to the
26       hosts configuration in nsswitch.conf.  The DNS-based name resolver  (in
27       the dns NSS service module) resolves them in the following fashion.
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29       If  the  name consists of a single component, that is, contains no dot,
30       and if the environment variable HOSTALIASES is set to  the  name  of  a
31       file, that file is searched for any string matching the input hostname.
32       The file should consist of lines made up of two  white-space  separated
33       strings,  the  first  of which is the hostname alias, and the second of
34       which is the complete hostname to be substituted for that alias.  If  a
35       case-insensitive match is found between the hostname to be resolved and
36       the first field of a line in the file, the substituted name  is  looked
37       up with no further processing.
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39       If  the  input  name  ends with a trailing dot, the trailing dot is re‐
40       moved, and the remaining name is looked up with no further processing.
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42       If the input name does not end with a trailing dot, it is looked up  by
43       searching  through  a  list of domains until a match is found.  The de‐
44       fault search list includes first the local domain, then its parent  do‐
45       mains with at least 2 name components (longest first).  For example, in
46       the domain cs.example.com, the name lithium.cchem will be checked first
47       as  lithium.cchem.cs.example  and  then  as  lithium.cchem.example.com.
48       lithium.cchem.com will not be tried, as there is only one component re‐
49       maining from the local domain.  The search path can be changed from the
50       default by a system-wide configuration file (see resolver(5)).
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SEE ALSO

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

61       This  page  is  part of release 5.12 of the Linux man-pages project.  A
62       description of the project, information about reporting bugs,  and  the
63       latest     version     of     this    page,    can    be    found    at
64       https://www.kernel.org/doc/man-pages/.
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68Linux                             2019-05-09                       HOSTNAME(7)
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