Determine the best Apache MaxClients parameter.

max_clients.sh

#!/bin/bash

# Copyright (c) 2012 Mark Caudill <mark@markcaudill.me>
#
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cat <<ABOUT
Apache processes usually get larger as time goes on so it's best to
run this after Apache has been running for a while or after a load
test (http://tools.pingdom.com/fpt/). This also means that running
this test multiple times in rapid succession will will yield drastically
different results.

ABOUT

# Get amount of free memory.
free_memory_apache_running=$(free -b | head -n2 | tail -n1 | awk '{print $4}')

# Get count of Apache child processes.
num_apache_procs=$(($(pgrep apache | wc -l) - 1))
if [[ $apache_procs -eq -1 ]]; then
    num_apache_procs=$(($(pgrep httpd | wc -l) - 1))
fi
if [[ $apache_procs -eq -1 ]]; then
    echo 'It seems that Apache may not be running. Unable to find any Apache processes.'
    exit 1
fi

# Stop Apache.
/etc/init.d/apache2 stop 2&>/dev/null || \
/etc/init.d/httpd stop 2&>/dev/null   || \
{ echo 'Unable to stop Apache. Exiting.' && exit 1; }

# Get amount of free memory.
free_memory_apache_shutdown=$(free -b | head -n2 | tail -n1 | awk '{print $4}')

# Start Apache.
/etc/init.d/apache2 start 2&>/dev/null || \
/etc/init.d/httpd start 2&>/dev/null   || \
echo 'Unable to start Apache. Oops.'

# Calculate results.
memory_per_apache_proc=$(( ( $free_memory_apache_shutdown - $free_memory_apache_running ) / $num_apache_procs ))
max_clients=$(( $free_memory_apache_shutdown / $memory_per_apache_proc ))
echo "Memory Per Apache Process: ${memory_per_apache_proc}B"
echo "MaxClients = FreeMemoryApacheShutdown / MemoryPerApacheProcess = $free_memory_apache_shutdown / $memory_per_apache_proc = $max_clients"