1HOSTNAME(7) Linux Programmer's Manual HOSTNAME(7)
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6 hostname - hostname resolution description
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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".
13 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.
19 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.
25 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.
35 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.
39 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)).
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52 getaddrinfo(3), gethostbyname(3), resolver(5), mailaddr(7), named(8)
53 IETF RFC 1123 ⟨http://www.ietf.org/rfc/rfc1123.txt⟩
55 IETF RFC 1178 ⟨http://www.ietf.org/rfc/rfc1178.txt⟩
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59 This page is part of release 4.15 of the Linux man-pages project. A
60 description of the project, information about reporting bugs, and the
61 latest version of this page, can be found at
62 https://www.kernel.org/doc/man-pages/.
63Linux 2017-05-03 HOSTNAME(7)