Find RAM size in Linux

When you order a dedicated server or cloud server with your web hosting provider, there is one thing you must check always when you first login into your system: your hardware must be exactly the same as ordered.

Lot of times, because of order mistakes, dedicated servers providers will give you less hardware resources than the ones you purchased. On this post, we will find out how to find RAM size in Linux / Unix operating systems with 5 useful commands.

How can I Find RAM size in Linux operating systems?

Here is the list of the top 5 commands that can be used to find LInux RAM size in Linux.

1. free command

The free command is the most classic terminal based tool to check memory usage on Linux / Unix operating systems.

[[email protected]:~]free
total used free shared buff/cache available
Mem: 32753636 9492448 1053688 603920 22207500 21961040
Swap: 8191996 1078724 7113272
[[email protected]:~]

The total OS RAM in bytes is 32753636, which can be translated to 32 GB of RAM installed on the system. The second colum called ‘used’ shows the the RAM used by the operating system, in this case around 9GB. Then you have the Free colum that is showing around 1GB, and the others called ‘shared’, ‘buffer/cache’ and ‘available’. It is normal to see lot of cached memory in the buff/cache on Linux operating systems, this memory can later be freed and used if really needed.
The last line belongs to the swap memory, which is reporting around 1GB of usage.

But this byte based numbers are not easy to read. Let’s use two useful parameters that can be added to the free command:

free -ht

Now we add -ht to the free command. -h is used to transform bytes into human readable units, and -t is used to display a line showing the column totals.

[[email protected]:~]free -ht
total used free shared buff/cache available
Mem: 31G 9.1G 1.0G 589M 21G 20G
Swap: 7.8G 1.0G 6.8G
Total: 39G 10G 7.8G
[[email protected]:~]

As you see on this output, now the free command is showing the information in sizes humans can read.

2. top command

Top command is one of my favourite and most used tools to quickly check out system performance, but it can also be used to get valuable hardware information.

Screenshot of top command showing an easy way to find RAM size in Linux
FIg. 01. Screenshot of top command showing an easy way to find RAM size in Linux

As you see on the screenshot, top command shows the total memory usage on an option called: KiB Mem (32753636 total in my case).
You will also be able to get your SWAP size, on the other line called KiB Swap (8191996 total in my case).
And same as the free command, you will get other kind of RAM information like buffer, cache and free available memory.

3. htop

htop is a good alternative to the classic top command, apart from RAM information, you will be able to get CPU and process usage. In clear words, htop is the top command but with an improved version which include colors, bar graphs for CPU/Mem/Swap, and a better way to deal/kill processes if needed.

Installing htop on Ubuntu/Debian

apt-get install htop

Installing htop on CentOS/RHEL

yum install htop -y

htop can be run simply by running:


Expected output:

htop command linux
Fig. 02. htop command output

As you see, the available RAM and SWAP usage is pretty clear, showed in GBs and with a clear bar.

4. vmstat

vmstat command along with the “s” parameter with show you memory uisage statistics, from there you will also be able to get total RAM memory and free memory.

Run this command:

vmstat -s

This is an output example on our server:

[[email protected]:~]vmstat -s
     32753636 K total memory
      9562108 K used memory
     11811520 K active memory
     16346200 K inactive memory
       927968 K free memory
            0 K buffer memory
     22263560 K swap cache
      8191996 K total swap
      1078724 K used swap
      7113272 K free swap
     70588049 non-nice user cpu ticks
      4283838 nice user cpu ticks
     24577630 system cpu ticks
   2023074528 idle cpu ticks
      4177230 IO-wait cpu ticks
            0 IRQ cpu ticks
      1063579 softirq cpu ticks
            0 stolen cpu ticks
   3076934802 pages paged in
   6491214798 pages paged out
       620025 pages swapped in
      1033879 pages swapped out
   4238671160 interrupts
   3149823550 CPU context switches
   1490028842 boot time
     10854442 forks
[[email protected]:~]

5. cat /proc/meminfo

The last way to find RAM size in Linux is by reading the /proc/meminfo file. For this we will use cat command, as you see below:

cat /proc/meminfo

Expected output:

cat /proc/meminfo output on Linux
Fig. 03. cat /proc/meminfo output on Linux

Find Hardware RAM Information

If you need to find out your full hardware information about the RAM you are using on your server, you can use the dmidecode command. It will show you valuable information about the installed RAM memory on your system.

Install dmidecode on Ubuntu/Debian

apt-get install dmidecode

Install dmidecode on CentOS/RHEL

yum install dmidecode -y

Now run this command:

dmidecode -t 17 | more

You will be able to get total RAM size, type (DDR2, DDR3, DDR4) and RAM speed, among other things, as you see on this screenshot of the server:

dmidecode is the best way to find ram hardware information on Linux
Fig. 04. Screenshot of dmidecode running. The best tool to find ram hardware information on Linux

Further reading:

About the Author: Santiago Borges

Experienced Sr. Linux SysAdmin and Web Technologist, passionate about building tools, automating processes, fixing server issues, troubleshooting, securing and optimizing high traffic websites.

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