Omarchy still won't install after CPU replacement. Other Linux distributions now work. Looking for ideas

[dollebrekel]

System details

DarkHero Z790, I9-14900KS, 128GB Ramm, RTX 5090

What's wrong?

Hi everyone,

I wanted to share an update on my installation issue and document everything I've tested so far.

Initially I suspected my hardware because multiple Linux distributions were failing, often with kernel panics or installer crashes. Windows was mostly usable, but Linux consistently failed.

Over the past weeks I tested almost everything I could think of:

Reset BIOS to Intel default settings.
Disabled any ASUS overclocking features.
No XMP or custom CPU settings.
Tested with different RAM configurations.
Tested multiple NVMe SSDs individually.
Tried installing on every SSD separately.
Tested multiple USB drives.
Recreated the installation media multiple times.
Tested the exact same USB stick on another PC, where it installed without any issues.
Tried Omarchy, Pop!_OS and Ubuntu.
Investigated PCIe/NVMe errors, kernel panics and filesystem.squashfs extraction failures.
Ran memory tests and many other diagnostics.

Eventually I sent the system in for RMA.

The service center performed their own hardware tests and the CPU failed an OCCT CPU stress test. My Intel 14900 CPU was replaced under the extended warranty.

After receiving the new CPU, the situation changed:

Ubuntu installs successfully.
Other Linux distributions also install and boot correctly.
The hardware now appears to be stable.

However...

Omarchy still refuses to install.

So the original hardware issue has been resolved, but there still seems to be something specific preventing Omarchy from installing on my system.

Current hardware:

ASUS ROG Maximus Z790 Dark Hero
Intel i9-14900 (replacement CPU)
128 GB DDR5
RTX 5090
Multiple NVMe SSDs (tested individually)

At this point I'm trying to determine whether this is:

something specific to Omarchy,
an incompatibility with my hardware,
or something else I'm overlooking.

Has anyone experienced something similar, or is there any debug information I can provide that would help narrow this down?

[dollebrekel]

Is there anything what I can do to help? Or does someone have any suggestions what I can try? I miss Omarchy so much! ;)

[dollebrekel]

Solved — root cause found: GRUB runs out of low memory (<4 GiB) on this board

Follow-up to my earlier report. This turned out to be two unrelated problems stacked on top of each other,
which is why it took so long to untangle.

Problem 1: a genuinely faulty CPU (already resolved)

Multiple distros were crashing, so the system went in for RMA. The service center's own testing showed the
i9-14900KS failing an OCCT CPU stress test, and it was replaced under the extended warranty. After that,
Ubuntu, Pop!_OS and other distros installed and booted fine.
But Omarchy still refused to install. So the hardware was fine — something else was going on.

Problem 2: not enough usable RAM below the 4 GiB boundary for GRUB

The failure was GRUB's mm.c:552: out of memory while loading the installer.

I dumped the memory map that my firmware hands to a bootloader (/sys/firmware/memmap) from a working Ubuntu
install on the same machine. The ROG Maximus Z790 Dark Hero exposes only:

Usable RAM below 4 GiB	712 MiB total
Split across	two blocks: 493 MiB and 219 MiB

The rest of that zone is reserved for PCIe/MMIO and firmware. Most boards leave 2–3 GiB there. Ironically it's the
128 GB of RAM and the RTX 5090 that squeeze this region so hard — huge BAR/MMIO windows eat into it.

Now the arithmetic:

• Omarchy's installer initramfs is 241 MB (measured on my USB stick)
• GRUB must place the initramfs as one contiguous block below 4 GiB
• That 241 MB has to fit inside the 493 MiB block alongside GRUB itself, the kernel, and firmware reservations

It doesn't fit. Hence the out-of-memory abort.
This explains every observation that previously made no sense:

• Ubuntu installs fine — its initrd is only 37 MB, so it fits with room to spare.
• The exact same USB stick installs Omarchy fine on my other PC — that board exposes far more low memory.
• It's not the stick, not the SSD, not the RAM, not the ISO. All of those tested clean, because none of them
  were the problem.

The fix: skip GRUB entirely and boot the kernel via its EFI stub

The kernel on the Omarchy ISO is built with an EFI stub flagged CAN_BE_LOADED_ABOVE_4G. If the firmware
launches the kernel directly, the initramfs can be placed anywhere in the full 128 GB and the 4 GiB boundary stops
mattering.

This explains every observation that previously made no sense:

• Ubuntu installs fine — its initrd is only 37 MB, so it fits with room to spare.
• The exact same USB stick installs Omarchy fine on my other PC — that board exposes far more low memory.
• It's not the stick, not the SSD, not the RAM, not the ISO. All of those tested clean, because none of them were the problem.

The fix: skip GRUB entirely and boot the kernel via its EFI stub

The kernel on the Omarchy ISO is built with an EFI stub flagged CAN_BE_LOADED_ABOVE_4G. If the firmware launches the kernel directly, the initramfs can be placed a | | |
|---|---|
| Usable RAM below 4 GiB | 712 MiB total |
| Split across | two blocks: 493 MiB and 219 MiB |

The rest of that zone is reserved for PCIe/MMIO and firmware. Most boards leave 2–3 GiB there. Ironically it's the 128 GB of RAM and the RTX 5090 that squeeze this
region so hard — huge BAR/MMIO windows eat into it.

Now the arithmetic:

• Omarchy's installer initramfs is 241 MB (measured on my USB stick)
• GRUB must place the initramfs as one contiguous block below 4 GiB
• That 241 MB has to fit inside the 493 MiB block alongside GRUB itself, the kernel, and firmware reservations

It doesn't fit. Hence the out-of-memory abort.

This explains every observation that previously made no sense:

This explains every observation that previously made no sense:

• Ubuntu installs fine — its initrd is only 37 MB, so it fits with room to spare.
• The exact same USB stick installs Omarchy fine on my other PC — that board exposes far more low memory.
• It's not the stick, not the SSD, not the RAM, not the ISO. All of those tested clean, because none of them were the problem.

The fix: skip GRUB entirely and boot the kernel via its EFI stub

The kernel on the Omarchy ISO is built with an EFI stub flagged CAN_BE_LOADED_ABOVE_4G. If the firmware launches the kernel directly, the initramfs can be placed anywhere in the full 128 GB and the 4 GiB boundary stops mattering.

I copied the kernel and initramfs from the USB stick to my existing EFI System Partition and created a one-shot boot entry (Secure Boot must be off):

# 1. Copy kernel + initramfs off the Omarchy USB onto the ESP
sudo mkdir -p /boot/efi/EFI/omarchy-installer
sudo cp /run/media/$USER/<ISO_LABEL>/arch/boot/x86_64/vmlinuz-linux \
        /run/media/$USER/<ISO_LABEL>/arch/boot/x86_64/initramfs-linux.img \
        /boot/efi/EFI/omarchy-installer/

# 2. Create the EFI-stub boot entry (adjust disk/part to your ESP)
sudo efibootmgr --create --disk /dev/nvme0n1 --part 1 \
  --label "Omarchy EFI-stub installer" \
  --loader '\EFI\omarchy-installer\vmlinuz-linux' \
  --unicode 'initrd=\EFI\omarchy-installer\initramfs-linux.img archisobasedir=arch archisolabel=<ISO_LABEL>'

# 3. Boot it once (replace XXXX with the entry number printed above)
sudo efibootmgr --bootnext XXXX

Reboot with the USB stick still plugged in — it still provides the installer filesystem; only the kernel/initramfs load path changed. The installer came straight up and Omarchy installed without a single issue.

After installation: keep the initramfs small

The installed system boots via Limine, which uses a combined kernel+initramfs image, so it can hit the same wall on firmware like this. Issues #5243 and #5980 look like the same class of failure. Right after the first successful boot I added a compression drop-in — this is a config file, so it applies to every future initramfs rebuild,
including kernel updates:

sudo tee /etc/mkinitcpio.conf.d/omarchy_compression.conf >/dev/null <<'EOF'
COMPRESSION="zstd"
COMPRESSION_OPTIONS=(-19 --long -T0)
EOF
sudo limine-mkinitcpio

How to check whether you have this problem

If your Omarchy install dies with out of memory in GRUB, run this from any working Linux install on the same machine:

for d in /sys/firmware/memmap/*/; do
  s=$(cat "$d/start"); e=$(cat "$d/end"); t=$(cat "$d/type")
  if [ "$t" = "System RAM" ] && [ $((s)) -lt $((4*1024**3)) ]; then
    echo "$(( (e - s) / 1024 / 1024 )) MiB usable at $s"
  fi
done

If the largest single block is smaller than your initramfs (ls -lh /path/to/usb/arch/boot/x86_64/initramfs-linux.img), this is your bug — and the EFI-stub route above should get you installed.

Summary

• Faulty CPU → replaced under RMA (real, but a separate problem)
• Omarchy failure → GRUB cannot fit a 241 MB initramfs into the 493 MiB of low memory this board exposes
• Workaround → boot the installer kernel directly via its EFI stub, bypassing GRUB
• Long-term → smaller/better-compressed initramfs, or an EFI-stub/systemd-boot path in the installer, would make this class of high-RAM + large-GPU board work out of the box

Happy to provide the full /sys/firmware/memmap dump or any other debug data if that's useful for a proper fix upstream.