On-Demand sar command usage (Ubuntu 18.04)

sar informations are recorded for each and every second, we can see the current sar data’s as well as historic datas from the sar file, two files are written in the default path of sar configuration. i.e., saXX and sarXX

Use sar -f will get the historic data , example sar -f /var/log/sa/sa10 -r, will show the memory usage for the month day10.