MaxClients sets a limit on the total number of server processes, or simultaneously connectedclients, that can run at one time. The main purpose of this directive is to keep a runawayApache HTTP Server from crashing the operating system. For busy servers this value should beset to a high value. The server's default is set to 150 regardless of the MPM in use. However, itis not recommended that the value for MaxClients exceeds 256 when using the prefork MPM.5.9.4. MinSpareServers and MaxSpareServersThese values are only used with the prefork MPM. They adjust how the Apache HTTP Serverdynamically adapts to the perceived load by maintaining an appropriate number of spare serverprocesses based on the number of incoming requests. The server checks the number of serverswaiting for a request and kills some if there are more than MaxSpareServers or creates some ifthe number of servers is less than MinSpareServers.The default MinSpareServers value is 5; the default MaxSpareServers value is 20. Thesedefault settings should be appropriate for most situations. Be careful not to increase theMinSpareServers to a large number as doing so creates a heavy processing load on the servereven when traffic is light.5.9.5. MinSpareThreads and MaxSpareThreadsThese values are only used with the worker MPM. They adjust how the Apache HTTP Serverdynamically adapts to the perceived load by maintaining an appropriate number of spare serverthreads based on the number of incoming requests. The server checks the number of serverthreads waiting for a request and kills some if there are more than MaxSpareThreads or createssome if the number of servers is less than MinSpareThreads.The default MinSpareThreads value is 25; the default MaxSpareThreads value is 75. Thesedefault settings should be appropriate for most situations. The value for MaxSpareThreads mustbe greater than or equal to the sum of MinSpareThreads and ThreadsPerChild, else theApache HTTP Server automatically corrects it.5.9.6. ThreadsPerChildThis value is only used with the worker MPM. It sets the number of threads within each childprocess. The default value for this directive is 25.5.10. ListenThe Listen command identifies the ports on which the Web server accepts incoming requests.By default, the Apache HTTP Server is set to listen to port 80 for non-secure Webcommunications and (in the /etc/httpd/conf.d/ssl.conf file which defines any secureservers) to port 443 for secure Web communications.If the Apache HTTP Server is configured to listen to a port under 1024, only the root user canstart it. For port 1024 and above, httpd can be started as a regular user.The Listen directive can also be used to specify particular IP addresses over which the serverChapter 10. Apache HTTP Server166
