‘free’ Commands to Check Memory Usage in Linux

Linux is one of the most popular open source operating system and comes with huge set of commands. The most important and single way of determining the total available space of the physical memory and swap memory is by using “free” command.

The Linux “free” command gives information about total used and available space of physical memory and swap memory with buffers used by kernel in Linux/Unix like operating systems.

 This blog provides some useful examples of “free” commands with options, that might be useful for you to better utilize memory that you have.

     

1. Display System Memory

Free command used to check the used and available space of physical memory and swap memory in KB. See the command in action below.

# free

total       used       free     shared    buffers     cached

Mem:       1021628     912548     109080          0     120368     655548

-/+ buffers/cache:     136632     884996

Swap:      4194296          0    4194296

2. Display Memory in Bytes

Free command with option -b, display the size of memory in Bytes.

# free -b

total       used       free     shared    buffers     cached

Mem:    1046147072  934420480  111726592          0  123256832  671281152

-/+ buffers/cache:  139882496  906264576

Swap:   4294959104          0 4294959104

 

3. Display Memory in Kilo Bytes

Free command with option -k, display the size of memory in (KB) Kilobytes.

# free -k

total       used       free     shared    buffers     cached

Mem:       1021628     912520     109108          0     120368     655548

-/+ buffers/cache:     136604     885024

Swap:      4194296          0    4194296

 

4. Display Memory in Megabytes

To see the size of the memory in (MB) Megabytes use option as -m.

# free -m

total       used       free     shared    buffers     cached

Mem:           997        891        106          0        117        640

-/+ buffers/cache:        133        864

Swap:         4095          0       4095

 

5. Display Memory in Gigabytes

Using -g option with free command, would display the size of the memory in GB(Gigabytes).

# free -g

total       used       free     shared    buffers     cached

Mem:             0          0          0          0          0          0

-/+ buffers/cache:          0          0

Swap:            3          0          3

 

6. Display Total Line

Free command with -t option, will list the total line at the end.

# free -t

total       used       free     shared    buffers     cached

Mem:       1021628     912520     109108          0     120368     655548

-/+ buffers/cache:     136604     885024

Swap:      4194296          0    4194296

Total: 5215924 912520 4303404

 

7. Disable Display of Buffer Adjusted Line

By default the free command display “buffer adjusted” line, to disable this line use option as -o.

# free -o

total       used       free     shared    buffers     cached

Mem:       1021628     912520     109108          0     120368     655548

Swap:      4194296          0    4194296

 

8. Display Memory Status for Regular Intervals

The -s option with number, used to update free command at regular intervals. For example, the below command will update free command every 5 seconds.

# free -s 5

total       used       free     shared    buffers     cached

Mem:       1021628     912368     109260          0     120368     655548

-/+ buffers/cache:     136452     885176

Swap:      4194296          0    4194296

 

9. Show Low and High Memory Statistics

The -l switch displays detailed high and low memory size statistics.

# free -l

total       used       free     shared    buffers     cached

Mem:       1021628     912368     109260          0     120368     655548

Low:        890036     789064     100972

High:       131592     123304       8288

-/+ buffers/cache:     136452     885176

Swap:      4194296          0    4194296

 

10. Check Free Version

The -V option, display free command version information.

# free -V

procps version 3.2.8