Linux.com: CLI Magic: Tracking System Performance with sar

“Sar is the ‘system activity report’ program found on *nix
systems. In Linux, you can usually find it in the sysstat package,
which includes programs and scripts to capture and summarize
performance data, then produce detailed reports. This suite of
programs can be useful in tracking down performance bottlenecks and
providing insight into how the system is used throughout the
day.

“Sadc (system activity data collector) is the program that
gathers performance data. It pulls its data out of the virtual
/proc filesystem, then it saves the data in a file (one per day)
named /var/log/sa/saDD where DD is the day of the month…”

Complete
Story