free Command in Linux
The free command in Linux displays the amount of free and used memory in the system. It displays the total amount of free and used physical and swap memory along with the buffer used by the kernel.
The free command assists in providing an overview of memory utilization by the system. It displays the system and swap memory in total, free, used, shared, buff/cache, and available columns.
Table of Contents
Here is a comprehensive guide to the options available with the free command −
Syntax of free Command
The syntax of Linux free command is as follows −
free [options]
The [options] field is used to specify options to display the output in different formats.
Options of free Command
The options of the free command are listed below −
| Flags | Options | Description |
|---|---|---|
| -b | --byte | It displays memory in bytes |
| -k | --kibi | It displays memory in kibibytes (KiB) |
| -m | --mebi | It displays memory in mebibytes (MiB) |
| -g | --gibi | It displays memory in gibibytes (GiB) |
| --tebi | It displays memory in tebibytes (TiB) | |
| --pebi | It displays memory in pebibytes (PiB) | |
| --kilo | It displays memory in kilobytes (kB) | |
| --mega | It displays memory in megabytes (MB) | |
| --giga | It displays memory in gigabytes (GB) | |
| --tera | It displays memory in terabytes (TB) | |
| --peta | It displays memory in petabytes (PB) | |
| -h | --human | It displays output in a human-readable format |
| -w | --wide | It switches to the wide mode (displays buffer and cache in separate columns) |
| -c count | --count count | It displays the output in count times |
| -l | --lohi | It shows the details in low and high memory statistics |
| -L | --line | It shows output in a single line |
| -s delay | --second delay | It keeps on displaying output after the specified delay |
| --si | It uses SI units (kilobytes, megabytes, gigabytes) instead of binary units (kibibytes, mebibytes, gibibytes) | |
| -t | --total | It displays an additional row showing a total of columns |
| -v | --committed | It displays a line showing the memory commit limit |
| --help | It displays help related to the free command | |
| -V | --version | It displays the command version |
Examples of free Command in Linux
This section demonstrates the usage of the free command in Linux with examples −
Displaying Memory
To display the memory usage in Linux, use the free command without any option −
free
It displays the output in bytes −
The output has six columns and two rows.
| Mem | It displays memory information of physical RAM |
| Swap | It displays the memory information of the swap (swap memory is memory on the hard drive used as virtual memory) |
The column details are given in the table below −
| total | It shows the total amount of memory |
| used | It shows the amount of memory currently in use |
| free | It shows the unused amount of memory |
| shared | It shows the memory shared by multiple processes |
| buff/cache | It shows the memory used by the kernel for buffer and cache |
| available | It shows available memory for new processes without a swap |
Displaying Memory in Various Formats
To display the usage of RAM and swap memory in mebibytes, use the -m option −
free -m
One mebibyte is equal to 1,048,576 bytes. Similarly, to display the output in gibibytes, use the -g option −
free -g
Displaying Memory in Megabytes
To display memory usage in the megabytes, use the --mega option −
free --mega
Displaying Memory in Gigabytes
To display RAM usage in gigabytes, use the --giga option −
free --giga
Displaying Memory in Human Readable Format
By default, the free command displays output in bytes. To display the free memory in a human-readable format, use the -h or --human format −
free -h
Displaying Memory in Wide Format
The wide format produces lines longer than 80 characters. It also displays the buffer and cache separately.
free -w
Displaying Memory Multiple Times
To display the free memory output multiple times at specified intervals, use the -s/--second and -c/--count options −
free -s 3 -c 2
The command displays the output twice, with a second output after three seconds.
Displaying Memory with Low & High Statistics
To display the output with low and high memory statistics, use the -l or --lohi option −
free -l
Displaying Memory in One Line
To display the output in one line, use the -L or --line option −
free -L
Displaying Memory with Commit Limit
The committed memory is a memory allocated for a system or applications. To display an additional row of committed memory, use the -v or --committed option −
free -v
Displaying Memory with Total
To display a row of Total, use the -t or --total options −
free -t
The above command adds a row of the total.
Conclusion
The free command in Linux displays the RAM and swap usage in the standard output. It is a powerful utility that shows memory usage in various formats. Moreover, it is used for managing resources and system performance improvement of the system.
In this tutorial, we explained the free command, its syntax, options, and usage in Linux with examples.