Isolating and Testing RAM Sticks in Ubuntu

This guide explains how to:

• Boot using only one RAM stick (by reserving other address ranges via `memmap=`)
• Test the remaining sticks with `memtester` inside the OS
• Cycle through all sticks, including the originally “known good”
• Reset to the normal configuration afterwards

If you are unsure which RAM stick works:

1. Power down and remove all but one stick
2. Insert into the primary DIMM slot (usually nearest the CPU — see your motherboard manual)
3. Attempt to boot
   • If the system posts and loads an OS, mark this stick bootable
   • If not, swap in another stick and repeat until one works

(For more on this isolation method, see [corsair.com](https://help.corsair.com/hc/en-us/articles/14238510858637-RAM-How-to-Test-RAM-Modules-for-Memory-Issues))

1. With only the bootable stick installed, boot Ubuntu.

2. Check stick size and slot mapping:

   sudo dmidecode --type memory

3. Record:

1. Size of the good stick (e.g. 8 GiB)
2. Number and sizes of all sticks when installed

1. Install all sticks. 2. Edit GRUB:

 
   sudo nano /etc/default/grub

3. In:

 <code>
   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
 </code>
 append:
 <code>
 memmap=<SIZE>$<START>
 </code>
 Where:
   * **SIZE** = total capacity of sticks to test
   * **START** = address immediately after the main stick’s range

 Example (8 GiB good stick, 24 GiB to test):
 <code>
 GRUB_CMDLINE_LINUX_DEFAULT="quiet splash memmap=24G$8G"
 </code>

4. Save, update GRUB, reboot:

 <code>
 sudo update-grub
 sudo reboot
 </code>   

Sidenote on update-grub: After editing /etc/default/grub, running update-grub ensures the new memmap parameter is written to /boot/grub/grub.cfg. Without this step, changes won’t apply on reboot.

Verification: After rebooting, check reserved memory with:

dmesg | grep -i memmap # Kernel log should show reserved regions free -h # Available RAM should reflect the exclusion

free -h

Should show only the good stick’s capacity as usable by the OS.

Install and run:

sudo apt install memtester
memtester <SIZE-TO-TEST>M 1

Where SIZE-TO-TEST ≈ reserved size.

Runtime note:

• `memtester` inside Ubuntu can complete a pass over a portion of RAM in minutes to under an hour, depending on size tested — it only tests memory the OS can allocate at runtime ([repair.wiki](https://repair.wiki/w/Raspberry_Pi_RAM_Test))
• `Memtest86+` at boot is much slower — several passes can take many hours or overnight ([rtech.support](https://rtech.support/docs/guides/memtest/memtest86)), but it is far more thorough

Once a stick passes the in‑OS test:

1. Shut down
2. Move this passing stick into the main slot
3. Move the previously main stick into the test slots
4. Update the `memmap` parameters accordingly (good stick’s size / address)
5. Repeat testing

This way, you can eventually test every stick, including the one you started with.

1. Edit `/etc/default/grub` and remove `memmap=…` 2. Update GRUB and reboot:

 <code bash>
 sudo update-grub
 sudo reboot
 </code>

3. Verify all RAM is detected:

 <code bash>
 free -h
 </code>

• ECC RAM: Check `journalctl -k | grep -i edac` for logged correctable errors
• Label defective sticks immediately
• If several sticks fail in the same slot, suspect the slot or motherboard
• See [corsair.com](https://help.corsair.com/hc/en-us/articles/14238510858637-RAM-How-to-Test-RAM-Modules-for-Memory-Issues) for more on physically testing one stick at a time