Ubuntu Tutorials - Herong's Tutorial Examples

∟Introduction to Ubuntu Systems

∟"free" - Display Free and Used Memory

This section provides a tutorial example on how to display free and used memory information using the 'free' command on Ubuntu systems.

Another important information about your Ubuntu system is the memory. You can use the "free" command to display memory statistics including free memory and used memory sizes. Here are some examples of "free" command output on my Ubuntu computer.

1. Display memory information using "free" with default options. The memory counts are displayed in units of kibibytes (KiB) (1,024 bytes). Note that a kibibyte (1,024 bytes) is slightly different than a kilobyte (KB) (1,000 bytes).

herong$ free
           total     used     free   shared  buff/cache   available
Mem:     3709516  1218952   652908   176128     1837656     2028376
Swap:     999420   828844   170576

The above output shows that:

• The system memory (RAM - Random Access Memory) capacity is 3,709,516 KiB.
• Only 1,218,952 KiB of RAM is truly used. So it has about 2,490,564 KiB available for applications to use.
• But some (1,837,656 KiB) of available RAM is used as temporary "buff/cache" space. So it has only 652,908 KiB truly free (not used at all).
• The system also configured with a 8,085,500 KiB swap file on the hard disk. It can be used as an extension to the RAM.

2. To control the unit, you can use "free -b | k | m | g" options.

herong$ free -m
           total     used     free   shared  buff/cache   available
Mem:        3622     1178      686      170        1757        1993
Swap:        975      807      168

3. Or you can use "free -h" to display counts in human readable formats. And add "-w" to separate "buff" and "cache".

herong$ free -h -w
        total    used    free   shared   buffers   cache   available
Mem:     3.5G    1.2G    684M     171M      141M    1.6G        1.9G
Swap:    975M    807M    168M

The output columns are defined as:

• total - Total installed memory (MemTotal and SwapTotal in /proc/meminfo)
• used - Used memory (calculated as total - free - buffers - cache)
• free - Unused memory
• shared - Memory used (mostly) by tmpfs
• buffers - Memory used by kernel buffers (Buffers in /proc/meminfo)
• cache Memory used by the page cache and slabs
• buff/cache - Sum of buffers and cache
• available - Estimation of how much memory is available for starting new applications, without swapping. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use

Table of Contents

 About This Book

►Introduction to Ubuntu Systems

 What is Ubuntu

 hostnamectl - Display System Information

►"free" - Display Free and Used Memory

 "who | w" - Logged-in Users and Their Running Commands

 GNOME - Desktop Interface and Environment

 Shell - The Command-Line Interpreter

 Process Management

 Memory Management

 Files and Directories

 APT (Advanced Package Tool)

 Network Connection on Ubuntu

 Internet Networking Tools

 SSH Protocol and ssh/scp Commands

 Administrative Tasks

 References

 Full Version in PDF/EPUB

"free" - Display Free and Used Memory - Updated in 2025, by Herong Yang