You used to be able to simply
dd /dev/mem back in the day, but no longer for security reasons (since kernel 2.6, IIRC).
The alternative is to either build the kernel yourself wih the option to let root do that (will edit with name later, on phone now) OR better, use fmem, a kernel module which creates a
/dev/fmem device pretty much meant for easy dumping.
fmem works great for me on 12.04. Just make sure you use the
run.sh file included in the tarball to load the module; do not use
----Memory areas: -----
reg00: base=0x000000000 ( 0MB), size= 1024MB, count=1: write-back
reg01: base=0x0c8800000 ( 3208MB), size= 2MB, count=1: write-combining
!!! Don't forget add "count=" to dd !!!
$ ls /dev/f*
/dev/fb0 /dev/fd0 /dev/fmem /dev/full /dev/fuse
$ sudo dd if=/dev/fmem of=/tmp/fmem_dump.dd bs=1MB count=10
10+0 records in
10+0 records out
10000000 bytes (10 MB) copied, 0.0331212 s, 302 MB/s