It is a little improper used the term error In the case “server reached MaxClients setting, consider raising the MaxClients setting“. It is more a notice by which the server administrator is warned that the limit has been exceeded “Maxclients”. It is true that exceeding this limit, leads to the instability of the Apache server and automatically to problems in the operation of web sites hosted on the server.
Maxclients it is Apache Directive which establishes the limit number of Requestthe what can be served simultaneously. All Requests (Requests) interrogations will be placed up to a number set by the value of the Directive ListenBacklog. In the case of servers using prefork, Maxclients It translates to the maximum number of processes launched to serve the Requests. The default limit of simultaneous reequests set by the Directive “Maxclients” it is 150. If we want to increase this limit, we must also consider the value of the Directive ServerLimit (establishes the maximum value for the life of the Apache processes). Serverlimit is set default to 256. Increasing MaxClients value, must be directly proportional to ServerLimit. 
Attention, however, because the increase of these two limits well beyond the implicitly set values, can prevent the start of the Apache server and the instability of the operating system. As much as the value ServerLimit It is larger, the more additional memory memory will be allocated.
If you meet the error “[error] server reached MaxClients setting, consider raising the MaxClients setting” (visible in Apache Error Log) and you are determined to change the values we talked about above, you can do this in two ways.
1. Using whm you can change the values in Main >> Service Configuration >> Apache Configuration >> Global Configuration (valid for servers that have installed CPANEL/WHM)
2. Change the values ServerLimit and Maxclients by editing the file httpd.conf. Usually, httpd.conf can be found in “/usr/local/apache/conf/httpd.conf”.
After changing the values in httpd.conf, restart the Apache server. (service httpd restart).
Stealth Settings – Fix Apache Error : server reached MaxClients setting.
