How to get to the memory profile of your linux system – free, top, vmstat (free versus top versus vmstat)

Overview

There are a myriad of tools and scripts that one runs on Linux to figure out the important question of how much free memory is left viz. “how much RAM is available?”.
And to answer the query, we use the following 3 tools that are almost guaranteed to be on all Linux systems and some Unix variants:
  1. free
  2. top
  3. vmstat

Free

The following command line demonstrates the invocation of the “free” command to display the amount of free and used physical and swap memory in the system in megabytes – borrowing the description from the man pages.

Explanation:

Free memory => free + buffers + cached = 155 + 314 + 1171 = 1640 =~ 1641 [the value in 3rd row. 4th col]

top

Explanation:

Free memory => 159100k + 321752k + 1199916k = 1680768k =~ 1641M (this is the value that we arrived at from the “free” coammand above]

vmstat

Using vmstat with the ‘s’ switch to display the memory statistics, we have the following:

Explanation:

Free memory => free memory + buffer memory + swap cache = 157704 + 322028 + 1201220 = 1680952 = 1641.554M =~ 1640M

Synopsis
The paths to discovering memory statistics are many but they ultimately lead to the same figures.  :-)

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