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209 lines
7.8 KiB
HTML
209 lines
7.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<TITLE>Apache Server Virtual Host Support</TITLE>
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</HEAD>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<BODY
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#000080"
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ALINK="#FF0000"
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>
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<!--#include virtual="header.html" -->
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<H1 ALIGN="CENTER">Virtual Host Support</H1>
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<STRONG>See Also:</STRONG>
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<A HREF="host.html">Non-IP based virtual hosts</A>
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<H2>What are virtual hosts?</H2>
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This is the ability of a single machine to be a web server for multiple
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domains. For example, an Internet service provider might have a machine
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called <CODE>www.serve.com</CODE> which provides Web space for several
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organizations including, say, <EM>smallco</EM> and <EM>baygroup</EM>.
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Ordinarily, these groups would be given parts of the Web tree on www.serve.com.
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So smallco's home page would have the URL
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<BLOCKQUOTE>
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http://www.serve.com/smallco/
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</BLOCKQUOTE>
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and baygroup's home page would have the URL
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<BLOCKQUOTE>
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http://www.serve.com/baygroup/
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</BLOCKQUOTE>
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<P>
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For esthetic reasons, however, both organizations would rather their home
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pages appeared under their own names rather than that of the service
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provider's; but they do not want to set up their own Internet links and
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servers.
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<P>
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Virtual hosts are the solution to this problem. smallco and baygroup would
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have their own Internet name registrations, <CODE>www.smallco.com</CODE> and
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<CODE>www.baygroup.org</CODE> respectively. These hostnames would both
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correspond to the service provider's machine (www.serve.com). Thus
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smallco's home page would now have the URL
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<BLOCKQUOTE>
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http://www.smallco.com/
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</BLOCKQUOTE>
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and baygroup's home page would would have the URL
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<BLOCKQUOTE>
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http://www.baygroup.org/
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</BLOCKQUOTE>
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<H2>System requirements</H2>
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Due to limitations in the HTTP/1.0 protocol, the web server <STRONG>must have a
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different IP address for each virtual host</STRONG>. This can be achieved
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by the machine having several physical network connections, or by use
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of a <A HREF="../misc/vif-info.html">virtual interface</A> on some operating
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systems.
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<H2>How to set up Apache</H2>
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There are two ways of configuring apache to support multiple hosts.
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Either by running a separate httpd daemon for each hostname, or by running a
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single daemon which supports all the virtual hosts.
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<P>
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Use multiple daemons when:
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<UL>
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<LI>The different virtual hosts need very different httpd configurations, such
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as different values for:
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<A HREF="../mod/core.html#servertype">ServerType</A>,
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<A HREF="../mod/core.html#user">User</A>,
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<A HREF="../mod/core.html#group">Group</A>,
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<A HREF="../mod/mod_mime.html#typesconfig">TypesConfig</A> or
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<A HREF="../mod/core.html#serverroot">ServerRoot</A>.
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<LI>The machine does not process a very high request rate.
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</UL>
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Use a single daemon when:
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<UL>
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<LI>Sharing of the httpd configuration between virtual hosts is acceptable.
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<LI>The machine services a large number of requests, and so the performance
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loss in running separate daemons may be significant.
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</UL>
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<H2>Setting up multiple daemons</H2>
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Create a separate httpd installation for each virtual host.
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For each installation, use the
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<A HREF="../mod/core.html#bindaddress">BindAddress</A> directive in the
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configuration
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file to select which IP address (or virtual host) that daemon services.
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<EM>E.g.</EM>,
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<BLOCKQUOTE><CODE>BindAddress www.smallco.com</CODE></BLOCKQUOTE>
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This hostname can also be given as an IP address.
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<H2>Setting up a single daemon</H2>
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For this case, a single httpd will service requests for all the virtual hosts.
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The <A HREF="../mod/core.html#virtualhost">VirtualHost</A> directive in the
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configuration file is used to set the values of
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<A HREF="../mod/core.html#serveradmin">ServerAdmin</A>,
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<A HREF="../mod/core.html#servername">ServerName</A>,
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<A HREF="../mod/core.html#documentroot">DocumentRoot</A>,
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<A HREF="../mod/core.html#errorlog">ErrorLog</A> and
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<A HREF="../mod/mod_log_config.html#transferlog">TransferLog</A> configuration
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directives to different values for each virtual host.
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<EM>E.g.</EM>,
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<BLOCKQUOTE><CODE>
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<VirtualHost www.smallco.com><BR>
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ServerAdmin webmaster@mail.smallco.com<BR>
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DocumentRoot /groups/smallco/www<BR>
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ServerName www.smallco.com<BR>
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ErrorLog /groups/smallco/logs/error_log<BR>
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TransferLog /groups/smallco/logs/access_log<BR>
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</VirtualHost><BR>
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<BR>
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<VirtualHost www.baygroup.org><BR>
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ServerAdmin webmaster@mail.baygroup.org<BR>
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DocumentRoot /groups/baygroup/www<BR>
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ServerName www.baygroup.org<BR>
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ErrorLog /groups/baygroup/logs/error_log<BR>
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TransferLog /groups/baygroup/logs/access_log<BR>
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</VirtualHost><BR>
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</CODE></BLOCKQUOTE>
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This VirtualHost hostnames can also be given as IP addresses.
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<P>
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Almost <STRONG>ANY</STRONG> configuration directive can be put
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in the VirtualHost directive, with the exception of
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<A HREF="../mod/core.html#servertype">ServerType</A>,
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<A HREF="../mod/core.html#user">User</A>,
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<A HREF="../mod/core.html#group">Group</A>,
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<A HREF="../mod/core.html#startservers">StartServers</A>,
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<A HREF="../mod/core.html#maxspareservers">MaxSpareServers</A>,
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<A HREF="../mod/core.html#minspareservers">MinSpareServers</A>,
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<A HREF="../mod/core.html#maxrequestsperchild">MaxRequestsPerChild</A>,
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<A HREF="../mod/core.html#bindaddress">BindAddress</A>,
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<A HREF="../mod/core.html#pidfile">PidFile</A>,
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<A HREF="../mod/mod_mime.html#typesconfig">TypesConfig</A>, and
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<A HREF="../mod/core.html#serverroot">ServerRoot</A>.
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<P>
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<EM>SECURITY:</EM> When specifying where to write log files, be aware
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of some security risks which are present if anyone other than the
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user that starts Apache has write access to the directory where they
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are written. See the <A HREF="../misc/security_tips.html">security
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tips</A> document for details.
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<P>
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<H2>File Handle/Resource Limits:</H2>
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When using a large number of Virtual Hosts, Apache may run out of available
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file descriptors if each Virtual Host specifies different log files.
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The total number of file descriptors used by Apache is one for each distinct
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error log file, one for every other log file directive, plus 10-20 for
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internal use. Unix operating systems limit the number of file descriptors that
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may be used by a process; the limit is typically 64, and may usually be
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increased up to a large hard-limit.
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<P>
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Although Apache attempts to increase the limit as required, this
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may not work if:
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<OL>
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<LI>Your system does not provide the setrlimit() system call.
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<LI>The setrlimit(RLIMIT_NOFILE) call does not function on your system
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(such as Solaris 2.3)
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<LI>The number of file descriptors required exceeds the hard limit.
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<LI>Your system imposes other limits on file descriptors, such as a limit
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on stdio streams only using file descriptors below 256. (Solaris 2)
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</OL>
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In the event of problems you can:
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<UL>
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<LI>Reduce the number of log files; don't specify log files in the VirtualHost
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sections, but only log to the main log files.
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<LI>If you system falls into 1 or 2 (above), then increase the file descriptor
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limit before starting Apache, using a script like
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<BLOCKQUOTE><CODE>
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#!/bin/sh <BR>
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ulimit -S -n 100 <BR>
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exec httpd</CODE></BLOCKQUOTE>
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</UL>
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The have been reports that Apache may start running out of resources allocated
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for the root process. This will exhibit itself as errors in the error log like
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"unable to fork". There are two ways you can bump this up:
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<OL>
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<LI>Have a <CODE>csh</CODE> script wrapper around httpd which sets the
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"rlimit" to some large number, like 512.
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<LI>Edit http_main.c to add calls to setrlimit() from main(), along the lines
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of
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<PRE>
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struct rlimit rlp;
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rlp.rlim_cur = rlp.rlim_max = 512;
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if (setrlimit(RLIMIT_NPROC, &rlp)) {
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fprintf(stderr, "setrlimit(RLIMIT_NPROC) failed.\n");
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exit(1);
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}
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</PRE>
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(thanks to "Aaron Gifford <agifford@InfoWest.COM>" for the patch)
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</OL>
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The latter will probably manifest itself in a later version of Apache.
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<!--#include virtual="footer.html" -->
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</BODY>
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</HTML>
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