How to Check Linux Memory Space

Brief

There are several commands to check linux memory space like free, top, vmstat, ps or etc. Explain free command in this time.

E.g.1

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           993M         98M        783M        6.8M        112M        776M
Swap:          1.0G          0B        1.0G

Checking free, it shows 783M against total 998M. It can be found there is enough memory space. At a glance, Swap total is exceeded but Swap used is 0 B.

E.g.2

$ free -h
              total        used        free      shared  buff/cache   available
Mem:           1.8G        1.1G        105M        469M        685M      

In this example. free is only 105M against total 1.8G. But Linux is decreasing disc I/O by allocating rest of memory to buffer/cached. In many cases, free is just 100M left. Practical memory space is 105M + 685M = 890M, so there is enough capacity.