| <html lang="en"> |
| <head> |
| <title>Notes on NSS Configuration File - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="NSS-Configuration-File.html#NSS-Configuration-File" title="NSS Configuration File"> |
| <link rel="prev" href="Actions-in-the-NSS-configuration.html#Actions-in-the-NSS-configuration" title="Actions in the NSS configuration"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Notes-on-NSS-Configuration-File"></a> |
| <p> |
| Previous: <a rel="previous" accesskey="p" href="Actions-in-the-NSS-configuration.html#Actions-in-the-NSS-configuration">Actions in the NSS configuration</a>, |
| Up: <a rel="up" accesskey="u" href="NSS-Configuration-File.html#NSS-Configuration-File">NSS Configuration File</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">28.2.3 Notes on the NSS Configuration File</h4> |
| |
| <p>Finally a few more hints. The NSS implementation is not completely |
| helpless if <samp><span class="file">/etc/nsswitch.conf</span></samp> does not exist. For |
| all supported databases there is a default value so it should normally |
| be possible to get the system running even if the file is corrupted or |
| missing. |
| |
| <p><a name="index-default-value_002c-and-NSS-3283"></a>For the <code>hosts</code> and <code>networks</code> databases the default value is |
| <code>dns [!UNAVAIL=return] files</code>. I.e., the system is prepared for |
| the DNS service not to be available but if it is available the answer it |
| returns is definitive. |
| |
| <p>The <code>passwd</code>, <code>group</code>, and <code>shadow</code> databases are |
| traditionally handled in a special way. The appropriate files in the |
| <samp><span class="file">/etc</span></samp> directory are read but if an entry with a name starting |
| with a <code>+</code> character is found NIS is used. This kind of lookup |
| remains possible by using the special lookup service <code>compat</code> |
| and the default value for the three databases above is |
| <code>compat [NOTFOUND=return] files</code>. |
| |
| <p>For all other databases the default value is |
| <code>nis [NOTFOUND=return] files</code>. This solution give the best |
| chance to be correct since NIS and file based lookup is used. |
| |
| <p><a name="index-optimizing-NSS-3284"></a>A second point is that the user should try to optimize the lookup |
| process. The different service have different response times. |
| A simple file look up on a local file could be fast, but if the file |
| is long and the needed entry is near the end of the file this may take |
| quite some time. In this case it might be better to use the <code>db</code> |
| service which allows fast local access to large data sets. |
| |
| <p>Often the situation is that some global information like NIS must be |
| used. So it is unavoidable to use service entries like <code>nis</code> etc. |
| But one should avoid slow services like this if possible. |
| |
| </body></html> |
| |