Oracle Linux: How to Calculate Memory Usage

APPLIES TO

Linux x86-64

Oracle Cloud Infrastructure

GOAL

This document describes how to calculate Linux memory usage.

SOLUTION

1. Calculate memory usage using SAR

$ sar -r 1 10
...
09:54:56 AM kbmemfree        kbmemused   %memused kbbuffers kbcached  kbcommit             %commit
09:54:57 AM    193624        7784500     97.57    389504    2280488   9644972               60.44
09:54:58 AM    193608        7784516     97.57    389504    2280456   9644972               60.44
09:54:59 AM    193312        7784812     97.58    389504    2280504   9644972               60.44
09:55:00 AM    193204        7784920     97.58    389508    2281068   9645356               60.45
09:55:01 AM    132436        7845688     98.34    389508    2281356   9659980               60.54
09:55:02 AM    127380        7850744     98.40    389516    2281440   9659520               60.53
09:55:03 AM    126976        7851148     98.41    389516    2281068   9659036               60.53
09:55:04 AM    126308        7851816     98.42    389516    2281068   9659036               60.53
09:55:05 AM    126744        7851380     98.41    389516    2281092   9657976               60.52
09:55:06 AM    187128        7790996     97.65    389516    2281092   9656576               60.52
Average:       160072        7818052     97.99    389511    2280963   9653240               60.49

To calculate free memory from Average value do:

kbmemfree + kbbuffers + kbcached = actual free memory on the system

Using above example: 

160072 + 389511 + 2280963 = 2830546KB thats around 2.69GB free memory.

2. Calculate memory usage using free command

$ free -m
           total       used       free     shared    buffers     cached
Mem:        7791       7623        167        0        380       2227
-/+ buffers/cache:       5016       2775         
Swap:         7791        655       7136

From above example, to get free memory on the system use: -/+ buffers/cache - free column