Compiling the Linux Kernel from Source on Ubuntu

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I recently went through the process of building the Linux kernel from source on Ubuntu, as part of a kernel development course I’ve been working through. Here’s a simple breakdown of how it went.

Why compile your own kernel?

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The distro-provided kernel works fine for everyday use, but if you’re getting into kernel development — testing patches, exploring new config options, or just understanding how the pieces fit together — building your own from source is a rite of passage. Here’s how I did it.

Step 1: Install the dependencies

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Before touching the source, you need the tools that actually build the kernel:

sudo apt update
sudo apt install build-essential libncurses-dev bison flex libssl-dev libelf-dev bc

Step 2: Clone the kernel source

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I grabbed the mainline kernel directly from kernel.org:

git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
cd linux

Note: Full clone (no –depth): ~8.7 GB full history back to 2005, all branches and tags –depth=1: ~2 GB — just the latest snapshot, no history. so if you have slow internet or limited space sure to use –depth=1 in cloning

Step 3: Start from your current config

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Rather than configuring a kernel from a blank slate, I copied the config of my currently running Ubuntu kernel into the source tree:

cp /boot/config-$(uname -r) .config

This gives the new kernel a sensible starting point instead of building everything from scratch.

Step 4: Update the config

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Since the new kernel version has options that didn’t exist when the old config was written, I ran:

make olddefconfig

This fills in sensible defaults for anything new. If I wanted to manually enable or disable specific features, I could also open the interactive menu:

make menuconfig

Step 5: Build it

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This is the part that takes a while:

make -j$(nproc)

-j$(nproc) tells make to use all available CPU cores, which speeds things up considerably. Depending on your machine, this can still take anywhere from 20 minutes to over an hour.

Step 6: Install modules and the kernel

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Once the build finished successfully:

su -c "make modules_install install"

On Ubuntu, this single command quietly does more than it looks like — it copies the new kernel into /boot, installs the kernel modules, and also triggers hook scripts that regenerate the initramfs and update GRUB automatically. That’s a Debian/Ubuntu-specific convenience; other distros like Arch require running those steps manually.

Step 7: Reboot

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sudo reboot

After rebooting, a quick check confirms the new kernel is running:

uname -r

Final thoughts

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The whole process is more approachable than it sounds — most of the “work” is just installing dependencies and waiting for the build to finish. The real value is in understanding why each step exists, not just running the commands.