Ubuntu 4GB Ram Limitation and Solution

Q. I’ve total 8 GB RAM installed in my dual boot Ubuntu Linux 8.10 (32 bit) version HP workstation. But free -m command only shows 3291 (3G) memory. How do I use 8GB RAM under Ubuntu Linux?

A. You need to install Physical Address Extension (PAE) aware kernel under 32 bit Ubuntu Linux. It is a feature of x86 and x86-64 processors that allows more than 4 Gigabytes of physical memory to be used in 32-bit systems.


Without PAE kernel, you should see something as follows:
$ free -m
Sample output:

             total       used       free     shared    buffers     cached
Mem:          3291        801       2489          0         95        342
-/+ buffers/cache:        363       2927
Swap:         1906          0       1906

You have two options here as follows:

Option # 1: Use 64 bit Ubuntu Linux

64 bit Linux kernel will take care of 4G or more memory. Just grab latest 64 bit version and install it.

Option #2: Install PAE enabled kernel

Open terminal and type the following command if you are using Ubuntu version Ubuntu v9.04 and earlier:
$ sudo apt-get update
$ sudo sudo apt-get install linux-headers-server linux-image-server linux-server

If you are using Ubuntu v9.10 (Karmic Koala) and above, enter:
$ sudo apt-get install linux-generic-pae linux-headers-generic-pae
Once kernel images installed, just reboot your workstation, type:
$ sudo reboot
After reboot, login into your system and type the following command to verify memory usage:
$ free -m
Sample output:

             total       used       free     shared    buffers     cached
Mem:          8105       1292       6812          0         38        483
-/+ buffers/cache:        770       7334
Swap:         1906          0       1906

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114 comments… add one
  • gilles Nov 9, 2011 @ 11:24

    It works like a charm for me.

  • Alex Nov 17, 2011 @ 18:44

    That’s great! Thanks a lot!!

  • Tornike Nov 22, 2011 @ 18:18

    I followed the second option, but after the ‘free -m’ command I still get 3GBs of RAM in the list of results while I have 4 installed. The ‘apt-get install linux-restricted-modules-server’ command listed the following:

    ‘Building dependency tree
    Reading state information… Done
    E: Unable to locate package linux-restricted-modules-server’

    I read some advice regarding restricted packages in comments above – is this related to that and what exactly should I do?

    Thanks in advance

  • Mian Kashif Ali Mar 6, 2012 @ 17:08

    thanx so much for this wonderful tutorial..

  • Mojtaba Apr 3, 2012 @ 7:10

    Thanks for your effort and time :)

  • croman Apr 10, 2012 @ 13:28

    Tnks its work, very good in vostro 1320 with Ubuntu 11.10

  • Paul Jul 23, 2012 @ 9:55

    Thanks a lot!!!

  • sadik Feb 2, 2015 @ 4:59

    ubuntu 10.04 (4+4) total 8 gb ram but show only 3.61 what is solution to show full 8 gb ram.

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