The sar command

The sar command gathers statistical data about the system.

Though it can be used to gather some useful data regarding system performance, the sar command can increase the system load that can exacerbate a pre-existing performance problem if the sampling frequency is high. But compared to the accounting package, the sar command is less intrusive. The system maintains a series of system activity counters which record various activities and provide the data that the sar command reports. The sar command does not cause these counters to be updated or used; this is done automatically regardless of whether or not the sar command runs. It merely extracts the data in the counters and saves it, based on the sampling rate and number of samples specified to the sar command.

With its numerous options, the sar command provides queuing, paging, TTY, and many other statistics. One important feature of the sar command is that it reports either system-wide (global among all processors) CPU statistics (which are calculated as averages for values expressed as percentages, and as sums otherwise), or it reports statistics for each individual processor. Therefore, this command is particularly useful on SMP systems.

There are three situations to use the sar command: