Chapter 7. Managing kernel command-line parameters with UKI

With UKI, systemd-boot, specifically systemd-stub, handles the kernel command-line parameters. The UKI delivered by Red Hat includes the basic kernel command-line parameter console=tty0 console=ttyS0.

You can add additional kernel command-line parameters by using UKI add-ons. Alternatively, you can generate your own UKI to contain any arguments you require.

You manage boot entries directly in UEFI NVRAM. This means they are no longer stored on disk. You can use tools such as kernel-bootcfg or efibootmgr to alter boot entries directly.

The following is an example of a boot entry:

Boot0001* redhat	HD(1,GPT,9192a707-8768-4c9f-bb11-fdd7c7e307e7,0x800,0x100000)/\EFI\redhat\shimx64.efi\EFI\Linux\ffffffffffffffffffffffffffffffff-6.12.0-174.el10.x86_64.efi

To add kernel command-line parameters, you can acquire officially signed add-ons delivered by Red Hat in the kernel-uki-virt-addons packages. These add-ons are signed by the same certificates as their associated UKIs. The default installation path is /lib/modules/$(uname -r)/vmlinuz-virt.efi.extra.d/.

If you need add-ons other than these or prefer signing them on your own, you can create them with tools such as systemd-ukify or dracut.

To change kernel command-line parameters for all boot entries, add the UKI add-ons to the global add-ons directory /boot/efi/loader/addons/.

To change kernel command-line parameters for a single UKI, manage the add-ons on a per-UKI basis. The revocation mechanism applies to UKI and its associated add-ons locally.

By default, UKIs are located at the following path:

/boot/efi/EFI/Linux/<machine_id>-<kernel_version>.efi

The effective add-ons designated to this UKI are located at the following path:

/boot/efi/EFI/Linux/<machine_id>-<kernel_version>.efi.extra.d/

To customize the Linux kernel, initial RAM disk, or initrd, and kernel command-line parameters, you can create your own UKI by using tools such as systemd-ukify or dracut.