Arch Linux

credo

Member

Registered: 2025-08-18

Posts: 3

[SOLVED] Rebooted into old (6.15.9 vs 6.16) kernel after pacman -Syu

(Can't copy+paste terminal output as the kernel mismatch means no network interfaces are working—nor USB ports—on the affected computer.)

Installed Arch about a week ago. It's rebooted plenty of times with no issue before the kernel upgrade. I ran

pacman -Syu

and rebooted into the wrong kernel. See command output showing the kernel version and boot files:

$ pacman -Qi linux | head -2
Name : linux
Version: 6.16.arch2-1

$ uname -a
Linux mycomputer 6.15.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Sat, 02 Aug 2025 01:20:06 +0000 x86_64 GNU/Linux

$ lsblk -f
...
nvme0n1
    nvme0n1p1 vfat FAT32 D998-760B
    nvme0n1p2 crypto_LUKS 2 758c6acd-7bde-4b99-9fb0-c6a4ef32df46
        cryptlvm LVM2_member LVM2 001 8MrKLo-...
            MyVolGroup-swap swap 1 ad66301d-f03a-4177-bf9b-94e6eb505f4b
            MyVolGroup-root ext4 1.0 a19a5068-4c41-471c-9064-4b81570812d5
            MyVolGroup-home ext4 1.0 aac8d38e-20e6-43a6-8a9f-53a2aae03361

$ cat /etc/cmdline.d/root.conf
rd.luks.name=758c6acd-7bde-4b99-9fb0-c6a4ef32df46=cryptlvm root=/dev/MyVolGroup/root

$ cat /proc/cmdline
rd.luks.name=758c6acd-7bde-4b99-9fb0-c6a4ef32df46=cryptlvm root=/dev/MyVolGroup/root

$ cat /etc/fstab
# /dev/mapper/MyVolGroup-root
UUID=a19a5068-4c41-471c-9064-4b81570812d5 / ext4 rw,relatime 0 1
# /dev/mapper/MyVolGroup-home
UUID=aac8d38e-20e6-43a6-8a9f-53a2aae03361 /home ext4 rw,relatime 0 2
# /dev/mapper/MyVolGroup-swap
UUID=ad66301d-f03a-4177-bf9b-94e6eb505f4b none swap defaults 0 0

$ cat /etc/mkinitcpio.conf
# comments not included
MODULES=( )
BINARIES=( )
FILES=( )
HOOKS=(base systemd autodetect microcode modconf kms keyboard sd-vconsole block sd-encrypt lvm2 filesystems fsck)

$ cat /etc/mkinitcpio.d/linux.preset
# comments not included
ALL_kver="/boot/vmlinuz-linux"
PRESETS=('default' 'fallback')
default_uki="/efi/EFI/Linux/arch-linux.efi"
fallback_uki="/efi/EFI/Linux/arch-linux-fallback.efi"
fallback_options="-S autodetect"

$ tree -a /efi/EFI
/efi/EFI
    Linux
        arch-linux.efi
        arch-linux-fallback.efi

$ tree -a /boot
/boot
    amd-ucode.img
    vmlinuz-linux

$ cat /etc/modules-load.d/vfat.conf
vfat
nls_cp437
nls_ascii

To my eye, the fstab, cmdline, and mkinitcpio files look the same as I configured them during installation (I set it up as an LVM on LUKS booting a UKI with systemd-boot). I already rebooted again with no effect (output above was collected after the latest reboot).

Last edited by credo (2025-08-18 16:13:41)

Whoracle

Member

Registered: 2010-11-02

Posts: 206

Re: [SOLVED] Rebooted into old (6.15.9 vs 6.16) kernel after pacman -Syu

On phone, so I'll be brief:

Your fstab did not mount nvme0n1p1 to anywhere. Mount that, reinstall the Linux package and see where it goes from there. Also, if it is that, fix your fstab to prevent that issue in the future.

credo

Member

Registered: 2025-08-18

Posts: 3

Re: [SOLVED] Rebooted into old (6.15.9 vs 6.16) kernel after pacman -Syu

For the sake of those finding this on their own troubleshooting journeys, I'll document what I did here. The response about the fstab reminded me of this tip from the wiki:

If the ESP is not mounted to /boot, make sure to not rely on the systemd automount mechanism (including that of systemd-gpt-auto-generator) during kernel upgrades. Always mount it manually prior to any system or kernel update, otherwise you may not be able to mount it after the update, locking you in the currently running kernel with no ability to update the copy of kernel on the ESP.

Alternatively preload the required kernel modules on boot, e.g.:

/etc/modules-load.d/vfat.conf

vfat
nls_cp437
nls_ascii

During installation, I was thrown off by the "Alternatively" wording, so I had created that vfat.conf file as described, thinking that was an alternative to mounting the ESP. I guess I assumed if systemd loaded that module, it would automount the ESP. When the system had booted successfully, I figured all was well.

To fix, I chrooted in from a live USB and updated the kernel:

$ cryptsetup open /dev/nvmen0p2 MyVolGroup
$ mount /dev/MyVolGroup/root /mnt
$ mount /dev/MyVolGroup/home /mnt/home # I don't think this is necessary
$ mount /dev/nvmen0p1 /mnt/efi
$ arch-chroot /mnt
$ pacman -S linux linux-firmware # I don't think linux-firmware is necessary
$ exit
$ umount -R

Now I boot into the correct kernel:

$ uname -a
Linux mycomputer 6.16.0-arch2-1 ...

In regard to the fstab, should I just append a line like this?

UUID=D998-760B                            /efi vfat defaults,nodev,nosuid,noexec,fmask=0177,dmask=0077 0      2

credo

Member

Registered: 2025-08-18

Posts: 3

Re: [SOLVED] Rebooted into old (6.15.9 vs 6.16) kernel after pacman -Syu

Luckily, there was another kernel update, so I could test this immediately. I updated my fstab, rebooted, updated the kernel, and rebooted again into the latest kernel. All is well.

$ cat /etc/fstab
# /dev/mapper/MyVolGroup-root
UUID=a19a5068-4c41-471c-9064-4b81570812d5	/         	ext4      	rw,relatime	0 1

# /dev/mapper/MyVolGroup-home
UUID=aac8d38e-20e6-43a6-8a9f-53a2aae03361	/home     	ext4      	rw,relatime	0 2

# /dev/mapper/MyVolGroup-swap
UUID=ad66301d-f03a-4177-bf9b-94e6eb505f4b	none      	swap      	defaults  	0 0

# /dev/nvmen0p1
UUID=D998-760B                                  /efi            vfat            defaults,nodev,nosuid,noexec,fmask=0177,dmask=0077 0 2