IOMMU: difference between "/etc/kernel/cmdline" and "/etc/default/grub"

[IStoleYourCoconut]

I had a roadblock today and figured it out, but I want to understand the difference. I configured now three systems with iommu and pci-passthrough. Everytime appending intel_iommu=on at /etc/kernel/cmdline was enough. Those were on a:

ASUS Prime Z590-P
MSI MEG Z590 ACE
ASUS B450M-K II

MSI MEG Z690 Unify - Did only work in /etc/default/grub to change it to: intel_iommu=on to GRUB_CMDLINE_LINUX_DEFAULT=”quiet intel_iommu=on”.

Why?

p.s. newest proxmox iso image8.1.4/ec5affc9e41f1d79, kernel 6.5.11-8-pve

 

[leesteken]

Because Proxmox uses different bootloaders for different root filesystems combined with different boot modes: Please read the first paragraph of the Host Bootloader section of the manual: https://pve.proxmox.com/pve-docs/pve-admin-guide.html#sysboot