Attempting to access RAM /dev/mem... says "Operation not permitted"

I am using Ubuntu 12.04

I read the following tutorial on how to access the contents of RAM in Linux....

http://www.rootninja.com/using-dd-to-search-for-strings-in-memory-or-devices/

Code:

dd if=/dev/mem | hexdump -C | grep “string to search for”

So, I run the code...

Code:

sudo dd if=/dev/mem | hexdump -C > NAMEOFOUTPUTFILEHERE.txt

And... it starts pumping out HEX code, until a few seconds later, where it says:

dd: reading `/dev/mem': Operation not permitted
2056+0 records in 
2056+0 records out
1052672 bytes (1.1 MB) copied, 0.44834 s, 2.3 MB/s

So basically.. I am able to get about 3.3 MB of RAM dump contents-- until the program stops, saying "Operation not permitted"

And so I am wondering why am I not able to dump the entire contents of RAM? Is this a deliberate limitation in Ubuntu, to stop malicious hackers? Or, is it something else? Does anybody know? Thanks

The linux kernel on your Ubuntu installation ship with a setting^* which limits RAM extraction to has 1 MB.

If you do not wish that you can either recompile the kernel without it (obvious caveeat: you are lowering security!) or you can download and insmod the forensic kernel module fmem to work around this. That provides a /dev/fmem device without any security.

As mentioned by Opello: you can also use strict-devmem=0 in the kernel cmdline.

^*: STRICT_DEVMEM=y (see e.g. /boot/config-KERNELVERSION)