I’ve total 8 GB RAM installed in my dual boot Ubuntu Linux 10.10 (32 bit) version, but free -m command only shows 3291 (3G) memory. How do I use 8GB RAM under Ubuntu Linux? I do 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:
$ sudo apt-get update
$ sudo sudo apt-get install linux-headers-server linux-image-server linux-server

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

Sean Michael Kerner writes – Recent years have seen the Ubuntu Linux
distribution, led by Canonical, experiencing rapid growth in both
users and features. With the upcoming Ubuntu 10.10 Maverick Meerkat
release, set for October, Ubuntu developers will continue to push the
boundaries further of both server and desktop Linux. Sitting at the
upper rung of Ubuntu’s engineering efforts is Matt Zimmerman,
Canonical’s CTO, who helps to lead Ubuntu’s technical direction.

http://www.linuxplanet.com/linuxplanet/reports/7169/1/

Steve Conklin, Canonical Kernel Engineer, announced on September 1, 2010 that a new Ubuntu Lucid proposed kernel was available. The Ubuntu kernel team has prepared a new proposed kernel for Lucid (2.6.32-25.43), containing a large number of fixes. This is a larger number of updates than we would usually push at one time, but processing of the upstream stable updates was delayed by a couple of security updates.

This kernel should fix a lot of issues, including this one that people have been asking about a lot. You will get this automatically if you have updates from lucid-proposed enabled. Note that if it breaks you get to keep all the pieces, so don’t try this on production machines. Please test against your favorite bugs in the changelog and provide feedback.

http://www.illruminations.com/post/1048745747/new-ubuntu-lucid-proposed-kernel