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12 Practical and Useful free command examples in Linux(RHEL/CentOS 7/8)

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In this article, we are going to look at the 12 Practical and Useful free command examples frequently used in Linux (RHEL/CentOS 7/8). free command is an open source utility frequently used in Linux Based Servers to display the total amount of free and used physical and swap memory in the System. It parses all the values from /proc/meminfo file. We will see the usage of free command in detail with examples in below sections.

SYNOPSIS

free [options]

10 Practical and Useful free command examples in Linux(RHEL/CentOS 7/8)

free command examples in Linux

Also Read: 10 Simple and Useful ntpdate command examples in Linux(RHEL/CentOS 7/8)

Example 1: How to Check free command version in Linux

If you want to check free command version then you need to use free -V command as shown below.

[root@localhost ~]# free -V
free from procps-ng 3.3.10

-V : Display version information.

Example 2: How to Check Free Memory in bytes

If you are looking to check free memory and used memory details in bytes then you need to use free -b command as shown below.

[root@localhost ~]# free -b
         total      used       free    shared  buff/cache available
Mem:  2933882880  318574592 2472501248 8978432 142807040  2460704768
Swap: 2147479552      0     2147479552

-b : Display the amount of memory in bytes. More on free command Man Page.

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total : Total installed memory.

used : Used memory (calculated as total - free - buffers - cache)

free : Unused memory (MemFree and SwapFree in /proc/meminfo).

shared : Memory used (mostly) by tmpfs.

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.

Example 3: How to List Free Memory Details in kilobytes

If you are looking to check free memory and used memory details in kilobytes then you need to use free -k command as shown below.

[root@localhost ~]# free -k
       total   used   free   shared buff/cache available
Mem:  2865120 310932 2414704  8768    139484   2403208
Swap: 2097148   0    2097148

-k : Display the amount of memory in kilobytes. This is the default. More on free command Man Page.

Example 4: How to Display Free Memory information in Megabytes

If you are looking to check free memory and used memory details along with the swap usage in megabytes then you need to use free -m command as shown below.

[root@localhost ~]# free -m
     total used free shared buff/cache available
Mem:  2797 303  2358    8      136       2347
Swap: 2047  0   2047

-m : Display the amount of memory in megabytes. More on free command Man Page.

Example 5: How to Check Free Memory in Gigabytes

If you are looking to check free memory and used memory details in gigabytes then you need to use free -g command as shown below.

[root@localhost ~]# free -g
     total used free shared buff/cache available
Mem:   2    0    2     0        0         2
Swap:  1    0    1

-g : Display the amount of memory in gigabytes. More on free command Man Page.

Example 6: How to Check Free Memory in Human Readable Format

If you want to check free memory stats in human readable format then you need to use free -h command as shown below.

[root@localhost ~]# free -h
      total used free shared buff/cache available
Mem:  2.7G  303M 2.3G  8.6M     136M      2.3G
Swap: 2.0G   0B  2.0G

-h : Show all output fields automatically scaled to shortest three digit unit and display the units of print out. More on free command Man Page.

Example 7: How to Check low and high memory Stats in Detail

If you want to check low and high memory stats in detail then you need to use free -l command as shown below.

[root@localhost ~]# free -l
      total   used    free  shared buff/cache available
Mem: 2865120 310932 2414700  8768    139488   2403208
Low: 2865120 450420 2414700
High:   0      0      0
Swap: 2097148  0    2097148

-l : Show detailed low and high memory statistics. More on free command Man Page.

Example 8: How to Show Total Memory in Linux in Gigabytes

If you want to show total memory which includes physical memory and swap space in gigabytes then you need to use free -t -g command as shown below.

[root@localhost ~]# free -t -g
      total used free shared buff/cache available
Mem:   2     0    2      0       0         2
Swap:  1     0    1
Total: 4     0    4

-t : Display a line showing the column totals.

-g : Display the amount of memory in gigabytes.

Example 9: How to Display Free Memory Stats After Every N Seconds

If you want to display free command stats after every N seconds then you need to use free -s N command as shown below. Since here we are trying to display continuous stats after every 3 seconds then you need to use free -s 3 command as shown below.

[root@localhost ~]# free -s 3
       total  used   free    shared buff/cache available
Mem:  2865120 311092 2414540 8768     139488    2403048
Swap: 2097148  0     2097148

      total    used   free   shared buff/cache available
Mem:  2865120 311092 2414540 8768    139488    2403048
Swap: 2097148   0    2097148

       total   used   free   shared buff/cache available
Mem:  2865120 311092 2414540 8768    139488    2403048
Swap: 2097148    0   2097148

-s : Continuously display the result delay seconds apart.

Example 10: How to Show wide output of free command in Linux

If you want to show the wide output of free command then you need to use free -w command as shown below. Here you will see buffers and cache output separately as compared to previous shown examples.

[root@localhost ~]# free -w
       total   used   free   shared buffers cache  available
Mem:  2865120 310984 2414640  8768   2116   137380 2403152
Swap: 2097148   0    2097148

-w : Switch to the wide mode.

Example 11: How to Check all the available options of free command in Linux

If you want to check all the options available with free command then you need to use free --help command as shown below.

[root@localhost ~]# free --help

Usage:
free [options]

Options:
-b, --bytes show output in bytes
-k, --kilo show output in kilobytes
-m, --mega show output in megabytes
-g, --giga show output in gigabytes
--tera show output in terabytes
--peta show output in petabytes
-h, --human show human-readable output
--si use powers of 1000 not 1024

Example 12: How to Check Man Page of free command in Linux

If you want to check the man page of free command then you need to use man free command as shown below.

[root@localhost ~]# man free
FREE(1) User Commands FREE(1)

NAME
free - Display amount of free and used memory in the system

SYNOPSIS
free [options]

DESCRIPTION
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The informa‐
tion is gathered by parsing /proc/meminfo. The displayed columns are:

total Total installed memory (MemTotal and SwapTotal in /proc/meminfo)

used Used memory (calculated as total - free - buffers - cache)

free Unused memory (MemFree and SwapFree in /proc/meminfo)

shared Memory used (mostly) by tmpfs (Shmem in /proc/meminfo, available on kernels 2.6.32, displayed as zero if not available)

buffers
Memory used by kernel buffers (Buffers in /proc/meminfo)

cache Memory used by the page cache and slabs (Cached and SReclaimable in /proc/meminfo)

buff/cache
Sum of buffers and cache

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