98 lines
4.3 KiB
HTML
98 lines
4.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Choosing the Right Maps</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node137.html">Using the passwd and </A>
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<B>Up:</B> <A HREF="node130.html">The Network Information System</A>
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<B> Previous:</B> <A HREF="node135.html">Setting up a NIS </A>
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<BR> <P>
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<H1><A NAME="SECTION0012600000">Choosing the Right Maps</A></H1>
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<P>
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<A NAME="nisnsswitch"></A>
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<A NAME="5336"></A>
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<A NAME="5145"></A>
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<P>
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Having made sure you can reach the NIS server, you have to decide which
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configuration files to replace or augment with NIS maps. Commonly, you
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will want use NIS maps for the host and password lookup functions. The
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former is especially useful if you do not run BIND. The latter permits
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all users to log into their account from any system in the NIS domain;
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this usually requires sharing a central /home directory between
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all hosts via NFS. It is explained detail in section-<A HREF="node137.html#nispasswd"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A>
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below. Other maps, like services.byname, aren't such
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a dramatic gain, but save you some editing work if you install any
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network applications that use a service name that's not in the
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standard services file.
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<P>
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Generally, you want to have some freedom of choice when a lookup
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function uses the local files, and when it queries the NIS server.
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NYS allows you to configure the order in which a function accesses these
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services. This is controlled through the /etc/nsswitch.conf file,
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which stands for <em>Name Service Switch</em> but of course isn't limited
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to the name service. For any of the data lookup functions supported by
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NYS, it contains a line naming the services to use.
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<P>
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<A NAME="5337"></A>
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<A NAME="5338"></A>
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The right order of services depends on the type of data. It is unlikely
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that the services.byname map will contain entries differing from those
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in the local services file; it may only contain more. So a good
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choice may be to query the local files first, and check NIS only if
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the service name wasn't found. Hostname information, on the other hand,
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may change very frequently, so that DNS or the NIS server should always
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have the most accurate account, while the local hosts file
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is only kept as a backup if DNS and NIS should fail. In this case,
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you would want to check the local file last.
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<P>
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The example below shows how to configure gethostbyname(2),
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gethostbyaddr(2), and getservbyname(2) functions as
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described above. They will try the listed services in turn; if a lookup
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succeeds, the result is returned, otherwise the next service is tried.
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<P>
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<P><P>
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<P>
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The complete list of services that may be used with an entry in the
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nsswitch.conf file is shown below. The actual maps, files,
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servers and objects being queried depend on the entry name.
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<P>
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<P><P>
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<P>
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Currently, NYS supports the following nsswitch.conf entries:
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hosts, networks, passwd, group,
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shadow, gshadow, services,
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protocols, rpc, and ethers. More entries
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are likely to be added.
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<P>
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Figure-<A HREF="node136.html#nisfigswitch"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A> shows a more complete example which
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introduces another feature of nsswitch.conf: the
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[NOTFOUND=return] keyword in the hosts entry tells
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NYS to return if the desired item couldn't be found in the NIS or DNS
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database. That is, NYS will continue and search the local files
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<em>only</em> if calls to the NIS and DNS servers failed for some other
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reason. The local files will then only be used at boot time and as a
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backup when the NIS server is down.
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<P>
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<P><A NAME="5339"></A><BR>
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<STRONG>Figure:</STRONG>
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<A NAME="nisfigswitch"></A>
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Sample nsswitch.conf file.
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<BR>
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<P>
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<P>
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<A NAME="5340"></A>
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node137.html">Using the passwd and </A>
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<B>Up:</B> <A HREF="node130.html">The Network Information System</A>
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<B> Previous:</B> <A HREF="node135.html">Setting up a NIS </A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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