How to find total physical memory (RAM) size on Linux?

We can often get away without checking for total memory usage on servers running Linux. However, sometimes we may want to know the total memory available on our servers. Luckily, there are various ways to accomplish this task. In this tutorial, I'll show you some of them.

Using free Command

The free command is the simplest among the various commands we'll encounter. It displays the current amount of physical and virtual RAM being utilized by your system. You can run the free utility without any flags to get an idea about how much RAM is currently being used by your system.

Basic Usage

$ free

             total        used        free      shared  buff/cache   available
Mem:       8021048     1320432     5689744      335556     1010872     6121932
Swap:            0           0           0

For better readability, use the -h flag to display output in human-readable format ?

$ free -h

              total        used        free      shared  buff/cache   available
Mem:          7.6Gi       1.3Gi       5.4Gi       318Mi       985Mi       5.8Gi
Swap:            0B          0B          0B

We have a total of 7.6 GB of RAM. Other useful options include -k (kilobytes), -m (megabytes), and -s for continuous monitoring ?

$ free -h -s 5

The -s flag means "seconds", so free will print out the RAM usage every five seconds. You can stop the program by pressing Ctrl+C.

Using vmstat Command

The vmstat program prints out free, buffered, and cached memory alongside swap space, CPU, I/O, and system information.

Basic vmstat Output

$ vmstat -w

--procs-- -----------------------memory---------------------- ---swap-- -----io---- -system-- --------cpu--------
       r  b         swpd         free         buff        cache   si   so    bi    bo   in   cs us sy id wa st
       1  0            0      5352900        56816      1053708    0    0   162    73  328 1087 18  4 78  0  0

For detailed memory statistics, use the -s flag ?

$ vmstat -s

      8021048 K total memory
      1564516 K used memory
       305336 K active memory
      1962636 K inactive memory
      5391588 K free memory
        58224 K buffer memory
      1006720 K swap cache
            0 K total swap
            0 K used swap
            0 K free swap

To extract only the total memory information ?

$ vmstat -s | grep -i 'total memory'

      8021048 K total memory

Using top Command

The top command displays real-time statistics about your computer's resources, including memory usage.

$ top

top - 15:18:13 up 57 min,  1 user,  load average: 3.40, 3.26, 2.04
Tasks: 138 total,   1 running, 137 sleeping,   0 stopped,   0 zombie
%Cpu(s): 17.2 us,  3.6 sy,  0.0 ni, 77.5 id,  0.3 wa,  0.9 hi,  0.5 si,  0.0 st
MiB Mem :   7833.1 total,   4665.9 free,   1782.3 used,   1384.8 buff/cache
MiB Swap:      0.0 total,      0.0 free,      0.0 used.   5324.5 avail Mem

The memory information appears in the fourth line, showing a total of 7833.1 MB of RAM installed.

Using dmidecode Utility

dmidecode is a utility that extracts hardware information from the DMI table (part of UEFI firmware). It can provide detailed information about your system's maximum supported RAM size and installed memory modules.

Installing dmidecode

On Ubuntu-based distributions ?

# apt install dmidecode

On RHEL, Fedora, or CentOS ?

# yum install dmidecode

On Arch-based distributions ?

# pacman -S dmidecode

Using dmidecode for Memory Information

To view memory array information, use DMI type 19 ?

# dmidecode --type 19

Getting SMBIOS data from sysfs.
SMBIOS 3.0.0 present.

Handle 0x0049, DMI type 19, 31 bytes
Memory Array Mapped Address
        Starting Address: 0x00000000000
        Ending Address: 0x001FFFFFFFF
        Range Size: 8 GB
        Physical Array Handle: 0x0044
        Partition Width: 1

This shows we have a single 8 GB RAM module installed.

Using /proc/meminfo Virtual File

The /proc directory contains virtual files with system information. The meminfo file provides detailed memory statistics.

$ cat /proc/meminfo | head -n 3

MemTotal:        8021048 kB
MemFree:         4542960 kB
MemAvailable:    5155668 kB

Bash Script Example

Here's a simple bash script to extract total RAM information ?

#!/bin/bash
total_ram() {
    local totalram=$(cat /proc/meminfo | grep -i 'memtotal' | grep -o '[[:digit:]]*')
    echo $totalram
}
ram_size=$(total_ram)
echo "Total RAM: $ram_size kB"

Make it executable and run ?

$ chmod +x totalram.sh
$ ./totalram.sh

Total RAM: 8021048 kB

Comparison of Methods

Conclusion

Linux provides multiple methods to check total physical memory, each serving different needs. The free command is quickest for basic information, while dmidecode offers detailed hardware specifications. Choose the method that best fits your requirements and access level.