This blogitem gives some usefull commands that I've been using frequently. Just as a reference...
Calculate the number of php5-cgi processess running:
ps aux | grep php5-cgi | grep -v "(root|grep)" | wc -l
Display process list of processnames including “php5″:
ps axo 'pid user cmd' | grep php5 | grep -v "(root|grep)"
Analyse apache access.log: Display top 10 ip client ip addresses (in order to trace a ddos attack):
tail access.log | cut -d ' ' -f 1 | sort | uniq -c | sort -n -b -r | head -10