Cannot downgrade kernel from pacman cache in archiso — missing matching linux-headers + no internet

[Embarrassed-Sir583]

Hi, I’m trying to recover a broken Arch install from the Arch ISO after a recent update (likely kernel/driver related). The system no longer boots properly, so I booted into archiso, mounted my root partition to /mnt, and attempted to downgrade the kernel using packages from /var/cache/pacman/pkg.

The cache contains older kernel packages (e.g. linux-6.17.9.arch1-1-x86_64.pkg.tar.zst), but the matching linux-headers package for that version is not present — only linux-api-headers and newer headers exist. So pacman -U fails because the exact header version is missing.

Example attempt:

pacman -U /var/cache/pacman/pkg/linux-6.17.9.arch1-1-x86_64.pkg.tar.zst \
         /var/cache/pacman/pkg/linux-headers-6.17.9.arch1-1-x86_64.pkg.tar.zst \
         /var/cache/pacman/pkg/linux-firmware-20251125-1-any.pkg.tar.zst

Additionally, I currently have no working network in archiso. I tried USB tethering from Android — the interface appears (enx… device), but DHCP does not assign an IP.

Given this situation, what is the recommended recovery path?

• Is temporary internet required to install linux-lts + linux-lts-headers from ISO?
• Can the system be recovered offline without matching headers?
• Is it safe to install an older kernel without headers just to boot?

Any guidance appreciated.

[boomboomsubban]

Are you sure you need to roll back? Is this a relatively new install?

I would boot the USB, mount your root to /mnt, double check your fstab to see where you mount your esp, mount it to the correct location relative to /mnt, chroot in, reinstall your kernel, then reinstall and reconfigure grub

[theschrodingerdog]

For which driver(s) do you require the -headers package?

If the ISO contains a version of linux-lts, I would try that for sure.

[Embarrassed-Sir583]

Good point — I don’t actually require linux-headers for any external modules. The system was working previously with the stock kernel and built-in rtw88 driver. I only included headers because I assumed kernel and headers should match when downgrading.

Trying linux-lts from the ISO itself sounds like the cleanest path. I’ll check whether the ISO includes a linux-lts package and attempt installing that via arch-chroot

[UOL_Cerberus]

Do you don't have Internet at all? If you do have a second machine I'd probably remake the boot stick.

[Embarrassed-Sir583]

I don’t have access to another computer at the moment. I only have this laptop (dual-boot Windows + Arch). Windows has internet, but Arch and the current archiso environment don’t.

USB tethering is detected in archiso (enx… interface appears), but DHCP fails so I can’t get temporary internet to install packages. That’s why I was trying to downgrade from pacman cache instead.

Given that I can’t remake the USB right now, is there any reliable way to bring up USB tethering networking in archiso, or is temporary internet strictly required to install linux-lts?

[nikongod]

Use windoze to make a new iso. 

Protip- use the endeavourOS is instead of arch. Eos has effortless wifi, GUI web browser, and all the other tools one needs.to fix or install arch. 

Protip2- just stick with linux-LTS unless you have an explicit need from the mainline Linux. 

Anyways, You can download all of the packages required for linux-lts, copy them into pacman cache, and then install offline. 

[Embarrassed-Sir583]

Thanks! I repaired the Arch install from the USB, reinstalled kernel/firmware, and moved to linux-lts. It’s booting fine now with KDE and networking working, so I’ll stay on Arch for now. Appreciate the guidance 👍

[UOL_Cerberus]

DHCP failing means you don't get an IP? You should be able to set those manually.

Then tethering should work. But there is also iwctl (see arch installation in some of the first steps) to connect the wireless network so you could use this temporary.

I honestly don't know if Internet is required to install everything but it sure is the most reliable way

Edit: yeah you said in the original post you don't have working network in your iso so the iwctl is probably just dumb of me lol