there are two possible sources for newer kernels: either a new self built

kernel (the recommended way - see building-own-kernels.md) or if there is a

newer kernel available in the release area of the kernel build info repo which

can happen from time to time with no real guarantee if and when it might happen.

the kernel build is either a tar.gz archive which needs to be unpacked as root

from the root directoy (here 5.19.1-stb-exy+.tar.gzn as an example):

cd / tar xzf /somepath/5.19.1-stb-exy+.tar.gz

in the archive are some files in /boot, dtb files (if they exist for the kernel)

in /boot/dtb-5.19.1-stb-exy+ and the kernel modules and some tools in

/lib/modules/5.19.1-stb-exy+ (the plus sign at the end of the kernel version is

there if any kind of patches got applied relative to the clean original linux

mainline kernel tree).

it is always recommended and in case of a luks encryted root filesystem even

reqired to rebuild the corresponding initramfs after installing a new kernel

via the following command:

initramfs-update -c -k 5.19.1-sty-exy+

if the kernel is the result of an own kernel build then everything should

already be in place.

this depends on the way a system is booted and is described for the different

boot types in the following subsections:

a new entry for new kernel version has to be created in the file

/boot/extlinux/extlinux.conf - the easiest way is to simply copy and paste

another entry and adjust the kernel version for it. it might be required to

adjust the DEFAULT entry in extlinux.conf as well - this is only required if

there is no boot menu accessible via kayboard/display or serial console during

boot.

once running the "update-grub" command as root should include the new kernel

into the grub boot menu. be aware: depending on the kernel version number it

might not be set as the defulat kernel to be booted and might need manual

selection at the grub boot prompt.

first a note regarding 32bit armv7l chromebooks: so far they are not using the

kpart kernel image based approach as described below (which is valid for all

64bit aarch64 chromebooks) - they are using u-boot instead, so the u-boot

section should apply. intel based chromebooks usually using some form of grub

booting, so the grub section should apply for those.

chromebook images can boot kernels from one of the two special kernel

partitions of the disk (the first two small partitions), but the kernel builds

usually only build a kernel, which can be booted from the first partition as

during the creation of the kpart kernel boot image the root filesystem defined

for the kernel is hard coded to "root=PARTUUID=%U/PARTNROFF=3" which will use

the partiton with the offset 3 from the partition of the booted kernel as root

filesystem. as the root filesystem on those images is on partition 4 the

kernel has to be in partition 1 to be able to find it (1+3 = 4). a new kpart

image needs to be built with an offset of 2 to be able to boot it for testing

purposes for instance from the second kernel boot partition.

to install a chromebook kernel in the kpart format it simply has to be written

to the first partition of the device the image had been installed on (sd card

or usb disk) with the linux dd command like for example (assuming mmcblk0 as

device):

dd if=/boot/vmlinux.kpart-xyz of=/dev/mmcblk0p1

or (assuming sda as device):

dd if=/boot/vmlinux.kpart-xyz of=/dev/sda1

please double check the device name the kernel is being written too beforehand

as the dd command will simply override what is there without asking and

without any extra checks.

chromebooks will always boot from the kernel boot partition with the highest

priority which is by default the first kernel boot partition of the images. it

is possible to change the priority to make the second partition the one with

the highest priority so that it will get booted automatically during the next

boot with the following command:

cgpt add -i 2 -S 0 -T 1 -P 15 /dev/mmcblk0

assuming /dev/mmcblk0 to be the device for the disk to be booted. this switch

of boot priorities is only valid for a single boot, i.e. booting from the

second kernel boot partition has to be requested via this command new each

time. more information about how to test boot new kernels on chromebooks can

be found in test-booting-a-kernel-on-chromebooks.txt ...