How to use free command on Linux

The free command provides information about unused and used memory and swap space on any computer running Linux or another Unix-like operating system.
In this article we will show you useful examples of free commands.
The basic syntax of free command is:

free [options]

Show system memory

If you want to see available space of physical memory and swap memory in KB type free on your terminal:

# free
             total       used       free     shared    buffers     cached
Mem:       1020224     909720     110504      22736      26916     134908
-/+ buffers/cache:     747896     272328
Swap:            0          0          0

Display memory in bytes, kilobytes, megabytes and gigabytes

To show all of the data in bytes type free in your terminal with -b options:

# free -b
             total       used       free     shared    buffers     cached
Mem:    1044709376  867233792  177475584   23498752   17244160  109359104
-/+ buffers/cache:  740630528  304078848
Swap:            0          0          0

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To show all of the data megabytes type free in your terminal with -m options:

# free -m
             total       used       free     shared    buffers     cached
Mem:           996        826        169         22         25        106
-/+ buffers/cache:        694        301
Swap:            0          0          0

To show all of the data gigabytes type free in your terminal with -g options:

# free -g
             total       used       free     shared    buffers     cached
Mem:             0          0          0          0          0          0
-/+ buffers/cache:          0          0
Swap:            0          0          0

Other free command options

If you want to see a total memory ( including the swap), use the -t option, which will display a total line as shown below.

# free -t
             total       used       free     shared    buffers     cached
Mem:       1020224     872744     147480      23888      27376     114620
-/+ buffers/cache:     730748     289476
Swap:            0          0          0
Total:     1020224     872744     147480

The -s options activates continuous polling delay seconds apart. For example, the following would provide new data every five seconds and display the output in megabits:

# free -ms 5

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

# free -mt
             total       used       free     shared    buffers     cached
Mem:           996        782        213         23         27        116
-/+ buffers/cache:        638        357
Swap:            0          0          0
Total:         996        782        213

For more information about free command type man free in your terminal.