File /etc/apache2/apache2.conf

# prefork MPM
# StartServers: number of server processes to start
# MinSpareServers: minimum number of server processes which are kept spare
# MaxSpareServers: maximum number of server processes which are kept spare
# MaxClients: maximum number of server processes allowed to start
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_prefork_module>
    StartServers            5
    MinSpareServers         5
    MaxSpareServers        10
    MaxClients             50
    MaxRequestsPerChild  1000
</IfModule>