The right way to read /dev/oldmem?

I am trying to read raw memory from the /dev/oldmem device. However, when I try to use the dd command to read from the device, I end up only with a file of size 4096 bytes or 4KB, rather than the complete memor开发者_如何学Cy dump.

The dd command I used was:

sudo dd if=/dev/oldmem of=/tmp/om

Here, /tmp/om should be a copy of the oldmem contents. But it is always coming out to be 4KB. Is there something wrong in my approach? Is there something that I missing here? My only goal is to view the complete memory of the system in raw format. That's all I want to do.

Please help me if you have any pointers/suggestions to make this work.

Thanks!