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| |
| <modulesynopsis metafile="perchild.xml.meta"> |
| |
| <name>perchild</name> |
| <description>Multi-Processing Module allowing for daemon processes serving |
| requests to be assigned a variety of different userids</description> |
| <status>MPM</status> |
| <sourcefile>perchild.c</sourcefile> |
| <identifier>mpm_perchild_module</identifier> |
| |
| <summary> |
| <note type="warning"> |
| This module is not functional. Development of this module is not |
| complete and is not currently active. Do not use |
| <module>perchild</module> unless you are a programmer willing to |
| help fix it. |
| </note> |
| |
| <p>This Multi-Processing Module (MPM) implements a hybrid |
| multi-process, multi-threaded web server. A fixed number of |
| processes create threads to handle requests. Fluctuations in |
| load are handled by increasing or decreasing the number of |
| threads in each process.</p> |
| </summary> |
| <seealso><a href="../bind.html">Setting which addresses and ports Apache |
| uses</a></seealso> |
| |
| <section id="how-it-works"><title>How it works</title> |
| <p>A single control process launches the number of child processes |
| indicated by the <directive module="perchild">NumServers</directive> |
| directive at server startup. Each child process creates threads as |
| specified in the <directive module="mpm_common">StartThreads</directive> directive. |
| The individual threads then |
| listen for connections and serve them when they arrive.</p> |
| |
| <p>Apache always tries to maintain a pool of <dfn>spare</dfn> or |
| idle server threads, which stand ready to serve incoming |
| requests. In this way, clients do not need to wait for new |
| threads to be created. For each child process, Apache assesses |
| the number of idle threads and creates or destroys threads to |
| keep this number within the boundaries specified by |
| <directive module="mpm_common">MinSpareThreads</directive> |
| and <directive module="mpm_common">MaxSpareThreads</directive>. |
| Since this process is very self-regulating, it is rarely |
| necessary to modify these directives from their default values. |
| The maximum number of clients that may be served simultaneously |
| is determined by multiplying the number of server processes |
| that will be created (<directive |
| module="perchild">NumServers</directive>) by the maximum |
| number of threads created in each process |
| (<directive module="mpm_common">MaxThreadsPerChild</directive>).</p> |
| |
| <p>While the parent process is usually started as root under |
| Unix in order to bind to port 80, the child processes and |
| threads are launched by Apache as a less-privileged user. The |
| <directive module="mpm_common">User</directive> and <directive |
| module="mpm_common">Group</directive> directives are used to |
| set the privileges of the Apache child processes. The child |
| processes must be able to read all the content that will be |
| served, but should have as few privileges beyond that as |
| possible. In addition, unless <a |
| href="../suexec.html">suexec</a> is used, these directives also |
| set the privileges which will be inherited by CGI scripts.</p> |
| |
| <p><directive module="mpm_common">MaxRequestsPerChild</directive> |
| controls how frequently the |
| server recycles processes by killing old ones and launching new |
| ones.</p> |
| |
| <section id="user-ids"><title>Working with different user-IDs</title> |
| <p>The <module>perchild</module> MPM adds the extra ability to |
| specify that particular processes should serve requests under |
| different user-IDs. These user-IDs can then be associated with |
| specific virtual hosts. You have to use one <directive |
| module="perchild">ChildPerUserID</directive> directive for |
| every user/group combination you want to be run. Then you can tie |
| particular virtual hosts to that user and group IDs.</p> |
| |
| <p>The following example runs 7 child processes. Two of them are run |
| under <code>user1</code>/<code>group1</code>. The next four are run |
| under <code>user2</code>/<code>group2</code> and the remaining |
| process uses the <directive module="mpm_common" |
| >User</directive> and <directive module="mpm_common">Group</directive> |
| of the main server:</p> |
| |
| <example><title>Global config</title> |
| NumServers 7<br /> |
| ChildPerUserID user1 group1 2<br /> |
| ChildPerUserID user2 group2 4 |
| </example> |
| |
| <p>Using unbalanced numbers of processes as above is useful, if the |
| particular virtual hosts produce different load. The assignment to |
| the virtual hosts is easily done as in the example below. In |
| conclusion with the example above the following assumes, that |
| <code>server2</code> has to serve about twice of the hits of |
| <code>server1</code>.</p> |
| |
| <example><title>Example</title> |
| NameVirtualHost *<br /> |
| <br /> |
| <VirtualHost *><br /> |
| <indent> |
| ServerName fallbackhost<br /> |
| # no assignment; use fallback<br /> |
| </indent> |
| </VirtualHost><br /> |
| <br /> |
| <VirtualHost *><br /> |
| <indent> |
| ServerName server1<br /> |
| AssignUserID user1 group1<br /> |
| </indent> |
| </VirtualHost><br /> |
| <br /> |
| <VirtualHost *><br /> |
| <indent> |
| ServerName server2<br /> |
| AssignUserID user2 group2<br /> |
| </indent> |
| </VirtualHost> |
| </example> |
| </section> |
| </section> |
| |
| <directivesynopsis location="mpm_common"><name>AcceptMutex</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>EnableExceptionHook</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>Group</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>PidFile</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>Listen</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>ListenBacklog</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>LockFile</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>MaxRequestsPerChild</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>MaxSpareThreads</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>MinSpareThreads</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>ScoreBoardFile</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>SendBufferSize</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>ServerLimit</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>StartThreads</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>ThreadLimit</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>ThreadStackSize</name> |
| </directivesynopsis> |
| <directivesynopsis location="mpm_common"><name>User</name> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>AssignUserID</name> |
| <description>Tie a virtual host to a user and group ID</description> |
| <syntax>AssignUserID <var>user-id</var> <var>group-id</var></syntax> |
| <contextlist><context>virtual host</context></contextlist> |
| |
| <usage> |
| <p>Tie a virtual host to a specific user/group combination. Requests |
| addressed to the virtual host where this directive appears will be |
| served by a process running with the specified user and group ID.</p> |
| |
| <p>The user and group ID has to be assigned to a number of children |
| in the global server config using the <directive module="perchild" |
| >ChildPerUserID</directive> directive. See the section above for a |
| <a href="#user-ids">configuration example</a>.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>ChildPerUserID</name> |
| <description>Specify user ID and group ID for a number of child |
| processes</description> |
| <syntax>ChildPerUserID <var>user-id</var> <var>group-id</var> |
| <var>num-children</var></syntax> |
| <contextlist><context>server config</context></contextlist> |
| |
| <usage> |
| <p>Specify a user ID and group ID for a number of child processes. |
| The third argument, <var>num-children</var>, is the number of child |
| processes to start with the specified user and group. It does |
| <em>not</em> represent a specific child number. In order to use this |
| directive, the server must be run initially as <code>root</code>. |
| If you start the server as a non-root user, it will fail to change |
| to the lesser privileged user.</p> |
| |
| <p>If the total number of child processes, found by totaling all of the |
| third arguments to all <directive>ChildPerUserID</directive> directives |
| in the config file, is less than <directive module="perchild" |
| >NumServers</directive>, then all remaining children will inherit the |
| <directive module="mpm_common">User</directive> and <directive |
| module="mpm_common">Group</directive> settings from the main server. |
| See the section above for a <a href="#user-ids">configuration |
| example</a>.</p> |
| |
| <note type="warning"><title>Security</title> |
| <p>Don't set <var>user-id</var> (or <var>group-id</var>) to |
| <code>root</code> unless you know exactly what you are doing, and |
| what the dangers are.</p> |
| </note> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>MaxThreadsPerChild</name> |
| <description>Maximum number of threads per child process</description> |
| <syntax>MaxThreadsPerChild <var>number</var></syntax> |
| <default>MaxThreadsPerChild 64</default> |
| <contextlist><context>server config</context></contextlist> |
| |
| <usage> |
| <p>This directive sets the maximum number of threads that will be |
| created in each child process. To increase this value beyond its |
| default, it is necessary to change the value of the <directive |
| module="mpm_common">ThreadLimit</directive> directive and stop and |
| re-start the server.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>NumServers</name> |
| <description>Total number of children alive at the same time</description> |
| <syntax>NumServers <var>number</var></syntax> |
| <default>NumServers 2</default> |
| <contextlist><context>server config</context></contextlist> |
| |
| <usage> |
| <p>The <directive>NumServers</directive> directive determines the number |
| of children alive at the same time. This number should be large enough to |
| handle the requests for the entire site. To increase this value beyond the |
| value of <code>8</code>, it is necessary to change the value of the |
| <directive module="mpm_common">ServerLimit</directive> directive and stop |
| and re-start the server. See the section above for a <a href="#user-ids" |
| >configuration example</a>.</p> |
| </usage> |
| </directivesynopsis> |
| |
| </modulesynopsis> |