156 lines
4.2 KiB
HTML
156 lines
4.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of HOSTNAME</TITLE>
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</HEAD><BODY>
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<H1>HOSTNAME</H1>
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Section: Linux Programmer's Manual (7)<BR>Updated: 2019-05-09<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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hostname - hostname resolution description
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<A NAME="lbAC"> </A>
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<H2>DESCRIPTION</H2>
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Hostnames are domains, where a domain is a hierarchical, dot-separated
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list of subdomains; for example, the machine "monet", in the "example"
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subdomain of the "com" domain would be represented as "monet.example.com".
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<P>
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Each element of the hostname must be from 1 to 63 characters long and the
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entire hostname, including the dots, can be at most 253 characters long.
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Valid characters for hostnames are
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<B><A HREF="/cgi-bin/man/man2html?7+ASCII">ASCII</A></B>(7)
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letters from
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<I>a</I>
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to
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<I>z</I>,
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the digits from
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<I>0</I>
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to
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<I>9</I>,
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and the hyphen (-).
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A hostname may not start with a hyphen.
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<P>
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Hostnames are often used with network client and server programs,
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which must generally translate the name to an address for use.
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(This task is generally performed by either
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<B><A HREF="/cgi-bin/man/man2html?3+getaddrinfo">getaddrinfo</A></B>(3)
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or the obsolete
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3).)
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<P>
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Hostnames are resolved by the NSS framework in glibc according
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to the
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<B>hosts</B>
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configuration in
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<B>nsswitch.conf</B>.
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The DNS-based name resolver
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(in the
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<B>dns</B>
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NSS service module) resolves them in the following fashion.
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<P>
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If the name consists of a single component, that is, contains no dot,
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and if the environment variable
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<B>HOSTALIASES</B>
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is set to the name of a file,
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that file is searched for any string matching the input hostname.
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The file should consist of lines made up of two white-space separated strings,
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the first of which is the hostname alias,
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and the second of which is the complete hostname
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to be substituted for that alias.
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If a case-insensitive match is found between the hostname to be resolved
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and the first field of a line in the file, the substituted name is looked
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up with no further processing.
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<P>
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If the input name ends with a trailing dot,
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the trailing dot is removed,
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and the remaining name is looked up with no further processing.
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<P>
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If the input name does not end with a trailing dot, it is looked up
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by searching through a list of domains until a match is found.
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The default search list includes first the local domain,
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then its parent domains with at least 2 name components (longest first).
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For example,
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in the domain cs.example.com, the name lithium.cchem will be checked first
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as lithium.cchem.cs.example and then as lithium.cchem.example.com.
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lithium.cchem.com will not be tried, as there is only one component
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remaining from the local domain.
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The search path can be changed from the default
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by a system-wide configuration file (see
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<B><A HREF="/cgi-bin/man/man2html?5+resolver">resolver</A></B>(5)).
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<A NAME="lbAD"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+getaddrinfo">getaddrinfo</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?5+nsswitch.conf">nsswitch.conf</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?5+resolver">resolver</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?7+mailaddr">mailaddr</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+named">named</A></B>(8)
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<P>
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IETF RFC 1123
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<P>
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IETF RFC 1178
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<A NAME="lbAE"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">DESCRIPTION</A><DD>
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<DT id="3"><A HREF="#lbAD">SEE ALSO</A><DD>
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<DT id="4"><A HREF="#lbAE">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:06:08 GMT, March 31, 2021
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</BODY>
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</HTML>
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