How to find a Linux server bottleneck

After all it seems that it was correct answer by dedicated server when it sees with this. It seems that I can somehow survive even if twice the access now comes. I am consuming more CPU resources etc. than I imagined, but within acceptable range.
How to easily identify the server and PC bottlenecks (Linux): ITpro Watcher
http://itpro.nikkeibp.co.jp/article/Watcher/20060404/234528/

Very easy to understand, logging in with SSH and trying out a command for the time being, roughly understandable by seeing the result. The following items are understood.

1. CPU utilization
2. Memory usage
3. Disk I / O
4. Number of TCP connections

For the time being, I will measure GIGAZINE in the peak time zone and I would like to prepare for future further increase in access.