The sar -r report below shows a number of statistics related to memory usage.
# sar -r 10 2 Linux 2.6.18-128.el5 (boson) 07/22/2012 05:01:32 PM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused %swpused kbswpcad 05:01:42 PM 22267292 14770512 39.88 377512 11499048 16778232 0 0.00 0 05:01:52 PM 22267360 14770444 39.88 377512 11499052 16778232 0 0.00 0 Average: 22267326 14770478 39.88 377512 11499050 16778232 0 0.00 0
In this display, kbmemfree is the amount of free memory in kilobytes, kbmemused is the amount of memory in use in kilobytes, %memused is the percentage of how much memory in use, kbbuffers is the amount of buffer space used by the kernel in kilobytes, kbcached is the amount of cached space used by the kernel, kbswpfree is the amount of free swapfile space, kbswpused is the amount of used swapfile space, %swpused is percentage of swap in use, and kbswpcad is the amount of cached swap memory. All measurements are in kilobytes except, ofr course, for the percentages. With -r 10 2, sar is showing us two intervals of ten seconds.
In this display, we can see that we have a whopping 22 Gbytes of free memory (the numbers shoiwn are in kilobytes).