How to build your own kernel on Slackware Linux
With all the noise lately about Dirty COW (CVE-2016-5195) and the lack of patched kernels from Slackware’s “Benevolent Dictator for Life”, I decided it was time to roll up the sleeves and get it done. Since Slackware doesn’t have a “sophisticated” build system and all that grease, it’s a trivial matter to step up to the plate and take responsibility for your own system. I’ll be using “vanilla-kernelversion” as my tag for the kernel and initrd. Also notice that I build my kernels as a normal user.
Download and verify the kernel source
Create a directory for building the new kernel:
mkdir ~/kernel; cd ~/kernel
Download the kernel source and signature from kernel.org:
wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.4.27.tar.xz wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.4.27.tar.sign
Decompress the archive:
unxz linux-4.4.27.tar.xz
Verify the .tar archive against the signature (this will fail as I don’t have the public key yet):
gpg2 --verify linux-4.4.27.tar.sign
Notice the “key ID” from the output of the previous step and download it from a key server:
gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 6092693E
Verify the .tar archive against the signature again and look for the “Good signature” message:
gpg2 --verify linux-4.4.27.tar.sign
Extract the tarball if everything checked out:
tar -xvf linux-4.4.27.tar
Enter the kernel source directory and clean the kernel tree:
cd linux-4.4.27 make clean && make mrproper
Configuring and compiling the kernel
There is obviously no reason to configure a brand new kernel from scratch when already running a generic stock Slackware kernel. Make sure you’re still in the kernel source directory and issue the following command to copy the running kernel configuration:
zcat /proc/config.gz > .config
For simplicity, I want all new configuration options to be set to their defaults. By using “olddefconfig” you’ll automatically chose the defaults without any manual handling:
make olddefconfig
To speed up the compiling, make sure to run make with the “-j” option (number of cores+1):
make -j9
Compiling kernel modules and installation
Everything from this point and onward is done as root. Switch to the root user and reenter the kernel source directory.
Proceed to install the kernel modules:
make modules_install
Copy the kernel to the boot directory and rename it (the location of the kernel image is the same for x86_64 and x86):
cp arch/x86/boot/bzImage /boot/vmlinuz-vanilla-4.4.27
Copy the System.map to the boot directory and rename it:
cp System.map /boot/System.map-vanilla-4.4.27
Copy the kernel .config to the boot directory and rename it:
cp .config /boot/config-vanilla-4.4.27
Enter the boot directory:
cd /boot
Delete the old System.map link:
rm System.map
Create a new System.map link:
ln -s System.map-vanilla-4.4.27 System.map
Initrd and LILO
I need to create an initial ramdisk to boot my kernel so I’ll use the mkinitrd command to create one. I’ll leave it to Slackware to identify which modules are needed by running mkinitrd_command_generator.sh with the “-k” parameter to specify the new kernel version. To avoid wiping my existing initrd I’ll name it initrd-vanilla-4.4.27. I’ll use the output from the generator to create the initrd (remember to modify the initrd name):
/usr/share/mkinitrd/mkinitrd_command_generator.sh -k 4.4.27 # Don't go copying the next line, that's an example. mkinitrd -c -k 4.4.27 -f ext4 -r /dev/sda2 -m jbd2:mbcache:ext4 -u -o /boot/initrd-vanilla-4.4.27.gz
To boot the new kernel, it needs to be added to LILO. Make sure to not remove the entry specifying your running Slackware kernel. If the new kernel doesn’t run, it’s practical to boot into a working one.
nano /etc/lilo.conf
Create a new entry for the new kernel (I’m using mine as default but that’s optional):
/****************************************** #etc/lilo.conf default = Vanilla image = /boot/vmlinuz-vanilla-4.4.27 root = /dev/sda2 read-only initrd = /boot/initrd-vanilla-4.4.27.gz label = Vanilla ******************************************/
Finally, run the lilo command and it’s all done.
lilo
But I’m using ELILO
Me too, replace the LILO section with this part: Configuring ELILO with a generic kernel on Slackware 14.2
