Pop!_OS 6.16.3 Kernel Fails to Mount EFI Partition Due to Missing iso8859-1 Charset Module

[arielsaghiv]

Description

I am experiencing boot failures on the Pop!_OS kernel version 6.16.3-76061603-generic on my Dell XPS 9310 laptop. The system repeatedly fails to mount the EFI system partition /boot/efi with error messages indicating that the required FAT codepage module for iso8859-1 charset is missing:

FAT-fs (nvme0n1p2): IO charset iso8859-1 not found

Attempts to manually load the nls_iso8859-1 kernel module result in:

modprobe: ERROR: could not insert 'nls_iso8859_1': Unknown symbol in module, or unknown parameter

Despite the module file existing in /lib/modules/6.16.3-76061603-generic/kernel/fs/nls/, it cannot be loaded due to what appears to be a kernel module ABI mismatch or packaging issue.

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Troubleshooting & Steps Taken

• Verified installed kernels and modules, including Pop!_OS kernels and Ubuntu generic kernels.
• Booting the equivalent Ubuntu 6.16.3 generic kernel works without any mount or charset errors.
• Reinstalled Pop!_OS 6.16.3 kernel image, modules, headers, and the linux-system76 meta-package multiple times.
• Rebuilt initramfs for 6.16.3 kernel explicitly, forcing inclusion of necessary codepage modules.
• Checked DKMS modules and rebuilt them, no resolution.
• Compared the nls_iso8859-1.ko module between Pop!_OS 6.16.3 and Ubuntu 6.16.3; both present but only Ubuntu kernel loads it correctly.
• Manual attempts to load the module in Pop!_OS 6.16.3 fail with unknown symbol errors.
• Booted an older working kernel (6.9.3-76060903) as temporary fallback.

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Current Impact

• The Pop!_OS 6.16.3 kernel in its current release form is not bootable due to missing or broken kernel module dependencies for FAT codepages.
• EFI partition mount failures lead to boot stalls and emergency mode.
• Users are forced to revert to older kernels or switch to Ubuntu generic kernels for stability.

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Recommendations for System76/Pop!_OS Team

• Investigate kernel build or packaging processes for 6.16.3 kernel, focusing on including correct codepage modules with matching symbol versions.
• Provide a fixed roll-out or patch release to restore EFI mount capability on affected hardware.
• Possibly coordinate with Ubuntu kernel maintainers if using Ubuntu sources to align kernel module builds.
• Improve testing to catch similar kernel initramfs or module loading errors before release.

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Attachments & Logs

• Kernel versions and installed modules lists (see discussion history).

• DKMS status outputs and rebuild attempts.

• Boot logs capturing the charset and FAT mounting errors.

[mirfilip]

I was hit by this bug today. Isn't this kind of critical as /boot/efi uses vfat and iso8859-1 charset?

OP provided a great writeup but I'll just that for those stuck, that it's possible to mount /boot/efi using a different charset, until iso8859-1 gets fixed:

1. sudo vim /etc/kernelstub/configuration
2. find an object referring to "esp_path": "/boot/efi" and add another key: "esp_options": "umask=0077,iocharset=cp437",. You can also add similar option to /etc/fstab for manual mount/unmount.

This way, you can boot this kernel and do some repair if your older kernel has problems.