Surviving kernel panic: diagnosing and working around boot regressions in CachyOS with Limine

Keeping a system updated is part of daily terminal work. But when you run a performance-focused rolling release distro like CachyOS, you will occasionally bump into an upstream regression. Today was one of those days.

I ran a routine upgrade that brought in the kernel 7.2 tree (linux-cachyos 7.2.2-1). After rebooting, my ASUS laptop (Intel Core HX with hybrid NVIDIA/Intel graphics) refused to boot. It froze solid before loading the initrd completely or handing off to userspace. Black screen, no prompt, no response.

Here is how I tracked down the cause in the logs, the quick mistake I made editing Limine by hand, and how I pinned the working kernel in pacman while reporting the bug upstream.

1. Initial triage: inspecting failures with journalctl#

Since the machine would not boot past the bootloader on kernel 7.2, I rebooted into the Limine menu and picked the older working image still on disk: 7.1.8-1.

With the desktop back up, I checked what failed during the broken boot. Running journalctl with -b -1 queries logs strictly from the previous boot attempt:

journalctl -b -1 | grep -iE "panic|error|fail|fault|kernel"

The logs pointed out the culprit immediately: ACPI DSDT lookup errors from the BIOS followed by failures in the asus-wmi module:

ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PC00.I2C1.TPL1], AE_NOT_FOUND
ACPI Error: AE_NOT_FOUND, During name lookup/catalog
asus_wmi: ASUS WMI generic driver loaded
asus_wmi: fan_curve_get_factory_default failed: -19
asus_wmi: using asus-wmi for asus::kbd_backlight
(udev-worker): Process '/bin/chmod 0666 /sys/class/leds/asus::kbd_backlight/brightness' failed with exit code 1.

What happened under the hood?#

The 7.2 branch changed how the kernel interprets ACPI tables and interacts with the asus-wmi platform driver. On this hardware, factory fan curve calls (fan_curve_get_factory_default) and keyboard backlight udev rules deadlocked against the I2C bus, stalling the kernel before root filesystems could mount.

Kernel 7.1.8-1 tolerated these ACPI table quirks and booted without issues.

2. The Limine trap and the blake2b error#

With 7.1.8-1 running fine, I wanted it as the default boot entry. CachyOS ships with Limine, which is fast and has clean configuration syntax.

I opened the config:

sudo nano /boot/limine.conf

I found the //linux-cachyos block pointing to the working kernel and did what anyone in a rush might do: cut the block and pasted it at the top, right below /+CachyOS.

I saved and rebooted. Limine immediately stopped with this message:

PANIC: Blake2b hash must be 128 characters long

Why the bootloader halted#

Limine validates configuration blocks and binaries with cryptographic checksums. Cutting and pasting inside nano broke the Blake2b hash string across lines, truncating it to fewer than the expected 128 hexadecimal characters.

Because the checksum length failed validation, Limine aborted boot early to prevent loading a corrupted setup.

The clean automated fix#

Instead of trying to fix raw hashes by hand, I booted through the fallback entry and let the system utilities or CachyOS manager rebuild the configuration:

# Recalculates checksums and rewrites limine.conf cleanly (or via CachyOS kernel manager)
sudo limine-enroll-config 2>/dev/null || sudo cachyos-kernel-manager

(If your installation uses automated initcpio hooks or the distribution's GUI, cachyos-kernel-manager safely rebuilds all bootloader entries without hash corruption).

The file was regenerated cleanly, the 128-character Blake2b hashes matched, and kernel 7.1.8-1 became the default entry again.

3. Hardening pacman: upgrading without pulling broken kernels#

With boot working, I still had over 430 packages waiting for updates (browsers, LLVM, Node.js, libraries). I wanted to update everything without pacman reinstalling kernel 7.2.2-1.

For the immediate run, I passed --ignore:

sudo pacman -Syu --ignore linux-cachyos,linux-cachyos-headers,linux-cachyos-bore,linux-cachyos-nvidia-open

Everything updated cleanly. To avoid typing that list on every daily update, I added the rule to /etc/pacman.conf:

# /etc/pacman.conf

# Hold back 7.2 kernel packages until ACPI/ASUS patches land
IgnorePkg = linux-cachyos linux-cachyos-headers linux-cachyos-bore linux-cachyos-nvidia-open

Pacman now shows that updates are available for those packages, but skips them until I remove the lock.

4. Submitting a clear report upstream#

Fixing my local machine gets my work back, but filing a bug report helps everyone with similar hardware.

I grabbed the package build details:

pacman -Qi linux-cachyos | grep -E "Name|Version|Build Date|Packager"

I attached the journalctl error logs from asus_wmi and ACPI, then opened Issue #1010 on the linux-cachyos GitHub repository detailing:

1. Exact hardware (ASUS with Intel HX and hybrid NVIDIA GPU).
2. The exact freeze point and DSDT/ACPI errors.
3. Proof that 7.1.8-1 runs without issues under the same setup.

Practical takeaways#

1. Do not edit boot hashes by hand: Limine strictly verifies configurations with 128-character Blake2b checksums. Use tools like limine-enroll-config instead.
2. journalctl -b -1 saves time: Checking logs from the failed boot right away stops you from guessing what happened.
3. Always keep a working fallback kernel: Having the previous stable kernel or LTS on disk means fixing a boot issue takes five minutes instead of hunting down a live USB.
4. Use IgnorePkg selectively: Lock only the broken packages so the rest of your system stays current.

Until the upstream fix lands in the repos, the workstation is running smooth and stable on 7.1.8-1.

See also

Infrastructure When battery optimization breaks the display manager: recovering from black screen in CachyOS with hybrid GPUs

Email Crontab kernel mechanics, Linux logging differences, and Exim mail spool maintenance

Linux Understanding tmpfs in Linux: does reducing temporary partitions really free up RAM?

This post is licensed under CC BY-NC.