Master Linux Memory Monitoring with the free Command and Its Options

free: Display Memory Usage

Function Description

The free command shows the system's physical memory and swap partition capacities, as well as used, free, shared, buffered, and cached memory amounts.

Command Syntax

free [options]

Option Meanings

The options are described below:

-b: display memory usage in bytes

-k: display memory usage in kilobytes

-m: display memory usage in megabytes

-g: display memory usage in gigabytes

-h: display memory information in a human‑readable format

-t: show total physical memory and swap capacity

-s: continuously monitor memory usage at specified intervals

-V: show version information

Reference Examples

Example 1

Human‑readable display of physical memory and swap capacity:

[root@cnLinuxer ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.8G        661M        471M        122M        685M        871M
Swap:          2.0G          0B        2.0G

Explanation of free output fields:

Mem section:

total: total physical memory

used: memory currently used

free: memory not allocated

shared: total memory shared among processes

buff/cache: size of disk cache

available: memory available for applications

Swap section:

total: total swap space

used: used swap space

free: free swap space

Example 2

Display memory usage as totals:

[root@cnLinuxer ~]# free -t -h
              total        used        free      shared  buff/cache   available
Mem:           1.8G        661M        471M        122M        685M        871M
Swap:          2.0G          0B        2.0G
Total:         3.8G        661M        2.5G

Example 3

Repeatedly print memory information:

# every 2 seconds until Ctrl+C
[root@cnLinuxer ~]# free -s 2

# every 3 seconds, print 5 times
[root@cnLinuxer ~]# free -s 3 -c5

Example 4

Show version information:

[root@cnLinuxer ~]# free -V
free from procps-ng 3.3.10