Introduction

The Linux free command outputs a summary of RAM usage, including total, used, free, shared, and available memory and swap space. The command helps monitor resource usage and allows an admin to determine if there’s enough room for running new programs.

In this tutorial, you will learn to use the free command in Linux.

Prerequisites

• A system running Linux
• Access to a terminal (Ctrl+Alt+T)

free Command Syntax

The free command takes the following syntax:

free [options]

[options] are discussed in the following section, and they are optional.

Running the free command without options outputs information about memory and swap, expressed in kibibytes:

Each column depicts the following:

Column	Description
total	Total RAM amount available on the system.
used	Memory currently in use by processes.
free	Unused memory, free.
shared	Memory shared by multiple processes.
buff/cache	Memory in use by the kernel (for buffers, page cache, and slabs).
available	Estimated memory amount available for starting new applications, excluding swap.

free gathers information by parsing the /proc/meminfo file.

free Command Options

Use options to customize and format the output. The free command accepts the following options:

Option	Description
-b, --bytes	Displays the memory amounts in bytes.
-k, --kibi	Displays the memory amounts in kibibytes. The command uses kibibytes by default.
-m, --mebi	Displays the memory amounts in mebibytes.
-g, --gibi	Displays the memory amounts in gibibytes.
--tebi	Displays the memory amounts in tebibytes.
--pebi	Displays the memory amounts in pebibytes.
-h, --human	Scales and formats the output to the shortest three-digit unit to produce a human-readable output.
-c, --count [count]	Updates the output [count] times.
-l, --lohi	Show detailed low and high memory statistics.
-s, --seconds [delay]	Continuously updates the output every [delay] seconds.
--si	Use power of 1000 (KB, MB, GB, etc.) instead of power of 1024 (KiB, MiB, GiB, etc.). For example, use --mebi --si to format the output in megabytes. Alternatively, use --kilo, --mega, --giga, and --tera.
-t, --total	Displays a line showing the column totals.
--help	Prints the help file.
-V, --version	Displays the program version.

free Command Examples

The following section shows different ways of using the free command.

Example 1: Output Memory Usage in Human Readable Format

The free command displays memory sizes in bytes by default, which isn’t practical in modern systems with large amounts of RAM. Make the free command output easier to read by specifying the -h option:

free -h

The command formats the output using the most appropriate unit for each value – KiB, MiB, GiB, etc.

Example 2: Continuously Show Memory Usage

Use the -s option to continually refresh the free command output and monitor an app’s resource usage. Invoke the free command with the -s option and specify the delay between each output refresh:

free -s2

The example above instructs free to refresh the output every two seconds. Stop the process with Ctrl+C.

Example 3: Specify Output Units

Specify a unit for displaying the memory values uniformly. Use powers of 1024 (the default) or 1000.

1. For powers of 1024, use:

• -b, --bytes
• -k, --kibi
• -m, --mebi
• -g, --gibi
• --tebi
• --pebi

For example:

free -m

The command produces an output with values expressed in mebibytes.

2. For powers of 1000, use:

• --kilo
• --mega
• --giga
• --tera
• --peta

For example:

free --mega

The output values are expressed in megabytes. Alternatively, use the --si option followed by the corresponding power of 1024 unit:

free --si --m

The output values are expressed in megabytes.

Example 4: Print Output Multiple Times

Specify the -c option to instruct free to automatically quit after refreshing the output a specific number of times. In the following example, the command prints the result four times:

free -c 4

After four updates, the command automatically quits.

Example 5: Separate Buff and Cache Columns

The buff and cache areas interact and depend on each other, so they are combined in the output. To see the buffers and cache columns separately, specify the -w option:

free -w

The output now shows a buffers column and a cache column separately.

Example 6: Show the Total Memory Column

The --total option instructs free to print a Total line that sums the values from the total, used, and free columns of the Mem and Swap lines.

free -h --total

In the example above we instructed free to show the Total line and produce the output in a human-readable format.

Example 7: Combine Options

Combine different free command options to automate and facilitate memory monitoring in a system. For example, combine the -s and -c options to make free produce an output several times with a delay between refreshes:

free -m -s3 -c4

The command runs four times with a three-second delay between updates and expresses the values in mebibytes.

Conclusion

This tutorial showed how to use the free command to monitor memory usage on a Linux system. The command allows system administrators to monitor RAM usage on a system or server. Therefore, it is a helpful utility for identifying a potential issue. Learn more about system memory by reading our article on the differences between Intel Optane, RAM, and SSD.

              total        used        free      shared  buff/cache   available
Mem:        8174520     5144520     144500      84500     2585504     2514500
Swap:       8388604          0     8388604