On Mon, 22 Mar 2021 14:11:58 +0200, Gidi Gal said: > I am new to kernel development, currently working on > https://kernelnewbies.org/FirstKernelPatch. I reached the step "Install > your changes" in "Modifying a driver on native Linux". I would like to > separate my developed kernel and my installed kernel and to switch between > the two in order to test my changes. I am not sure that my tutorial > explains how to do that.
Well... the first rule of thumb is to make sure that your kernel release name will be different one way or another. CONFIG_LOCALVERSION is a good way to ensure it, while linux-next kernels and git-bisect kernels have their own way of naming themselves. It's also what shows up in uname -r. What I have in /boot at the moment: [/boot] ls vmlinuz-* vmlinuz-5.10.0-0.rc6.20201204git34816d20f173.92.fc34.x86_64 vmlinuz-5.10.0-rc4-next-20201117-dirty vmlinuz-5.11.0-rc3-next-20210114-dirty vmlinuz-5.10.0-next-20201215 vmlinuz-5.10.0-rc6-next-20201203 vmlinuz-5.12.0-rc1-next-20210302-dirty vmlinuz-5.10.0-next-20201223-dirty vmlinuz-5.10.0-rc6-next-20201207 vmlinuz-5.12.0-rc2-next-20210309-dirty vmlinuz-5.10.0-rc1-00257-gcf9446cc8e6d-dirty vmlinuz-5.10.0-rc7-next-20201208 vmlinuz-5.8.0-next-20200807 vmlinuz-5.10.0-rc1-next-20201030 vmlinuz-5.11.0-rc2-next-20210105-dirty vmlinuz-5.8.0-rc1-next-20200616 Each has a matching config-, System.map-, and initramfs- file in /boot, a grub2 config entry in /boot/loader/entries/, and the loadable modules in subdirectories under /lib/modules/`uname -r`. So if you back up /boot and /lib/modules, you should be able to recover from any issues. Note that on many systems, /boot is ext4, but there's a /boot/efi that's vfat that kernel installs shouldn't be touching, but you want a copy in case an update of grub goes astray... This is probably a good time to back up your *entire* system, because lots of Bad Things can happen even when you're not testing a new kernel. If you want to double-check what your just-built kernel is called, you can use 'make kernelrelease' to tell you. As long as that's different from any installed kernel, you shouldn't have any issues with files getting overlaid. 'make install' will look for a script 'installkernel' that does some of the heavy lifting, like building an initramfs, adding grub entries, and the like. That usually lives in /sbin/installkernel, but if you create your own and have it before /sbin in $PATH, it will get used.
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