Commands to detect a flood or DOS?

Hi:
For the linux gurus here, just wondering, what are some useful commands to detect in real time a possible mini Apache flood or DOS? I see big bandwidth spikes at times throughout the day. One useful command I type is:

netstat -apn|grep :80|awk '{print $5}'|sort

to see the # of connections open by a particular IP. Any other useful commands? Thanks,

 

 

 

 

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