Is it possible to tell ubuntu to use only one memory chip, if the computer has two?

Solution 1:

memtest

FIRST, go to https://www.memtest86.com/ and download/run their free memtest to test your memory. Get at least one complete pass of all the 4/4 tests to confirm good memory. This may take a few hours to complete.

I suspect that memtest will fail. Remove your new SODIMM/DIMM and re-run memtest. If it passes, remove the passed SODIMM/DIMM, reinsert the other SODIMM/DIMM by itself, and re-run memtest.

badram

See How to install Ubuntu on a laptop with soldered RAM module that has damaged cells

If you look in /etc/default/grub, you'll find a GRUB_BADRAM= parameter where you can identify what bad memory locations there are.

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

Source: https://help.ubuntu.com/community/BadRAM#BADRAM_setting_in_Grub2

BADRAM setting in Grub2

The GRUB2 config file in Natty has a line for configuring kernel bad ram exclusions. So, I will assume that is the preferred way of mapping out a section of memory that is showing errors. The line I set was

GRUB_BADRAM="0x7DDF0000,0xffffc000" 

The suggested way on every web site I could find was to set this was to run memtest86 and let it show you the BadRAM settings. memtest86 gave me a page of stuff I would have had to enter. I could see that all the addresses were in one 16K block, so I just wanted to map that 16K block out of action. Here is how I generated the correct entry.

The first parameter is easy. That is the base address of the bad memory. In my case, I could see that all the bad addresses were greater than 0x7DDF0000 and less than 0x7DDF4000. So, I took the beginning of the 16K block as my starting address.

The second parameter is a mask. You put 1s where the address range you want shares the same values and 0s where it will vary. This means you need to pick your address range such that only the low order bits vary. Looking at my address, the first part of the mask is easy. You want to start with 0xffff. For the next nibble, I will explain with bit maps. I want to range from 0000 to 0011. So, the mask for badram would be 1100 or a hex c. The last 3 nibbles need to be all 0s in the mask, since we want the entire range mapped out. So, we get a total result of 0xffffc000.

After setting this line in /etc/default/grub, I ran sudo update-grub and rebooted and my bad memory was no longer being used. No kernel patches are needed to map out bad memory using this method.

Update #1:

If memory errors don't show up in lower memory, you can add the "mem=##MB" kernel option to temporarily disable memory above that point. Ex: According to memtest86, my stick of memory has errors between 315MB and 325MB. By adding "mem=314MB" I tell the kernel to pretend I only have 314MB. My system will be stable enough to build the patch, at which point I can pass a parameter to ONLY skip the section between 315MB and 325MB (this providing me 502MB of usable memory).

ie: Boot Ubuntu Live, at GRUB menu, hit e to enter edit mode, use the arrow keys to find "quiet splash", change to "quiet splash mem=2048MB", CTRL+x or F10 to continue booting.