KernelNewbies:

Developing on a native Linux platform

These instructions assume you're running a varient of Ubuntu (like [http://www.ubuntu.com/download/desktop/thank-you?distro=desktop&bits=64&release=lts 12.04 LTS]).

Short cut

If you're too lazy to read through this entire tutorial, and you've just installed a new Ubuntu 12.04 install, you can run [http://kernelnewbies.org/OPWfirstpatchSetup?action=AttachFile&do=get&target=kernel-dev.sh this bash script] instead. Warning: This script will install packages, change grub files, and download and install a new Linux kernel. Please run it as under your username, not as root.

Install some packages

First, open a terminal. Click the ubuntu logo at the top left corner and type "terminal". Click the terminal screen icon.

Next, run this command:

sudo apt-get install vim libncurses5-dev gcc make git exuberant-ctags

Setup your Linux kernel code repository

Once that finishes, run these two commands:

mkdir -p git/kernels
cd git/kernels

Then use the revision control system called [http://git-scm.com/ git] to clone Linus Torvalds' repository:

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

That's going to take a while. Why don't you read up on [http://lwn.net/Kernel/LDD3/ Linux Device Drivers] in the meantime? The first couple of chapters, especially the ones on kernel modules will be useful.

Next, change into the linux directory:

cd linux

Now you need to compile the kernel. The first step is setting up your kernel configuration.

Setting up your kernel configuration

Many kernel drivers can be turned on or off, or built as modules. The .config file in the kernel source directory determines which drivers are built. When you download the source tree, it doesn't come with a .config file. You have several options on generating a .config file. The easiest is to duplicate your current config.

Duplicating your current config

If you're trying to see if a bug is fixed, you probably want to duplicate the configuration on your running kernel. That config file is stored somewhere in /boot/. There might be several files that start with config, so you want the one associated with your running kernel. You can find that by running uname -a and finding the config file that ends with your kernel version number. Copy that file into the source directory as .config. Or just run this command:

cp /boot/config-`uname -r`* .config

Changing your config

If you need to make any changes to your configuration, run this command to silently update any new configuration values to their default:

make olddefconfig

If you need to make changes, you can run:

make menuconfig

This requires the ncurses library to be installed.

Building the kernel

Run

make

Or, if you have a multi-core processor, run

make -jX

Where X is a number like 2 or 4. If you have a dual core, 2 or 3 might be good. Quad core, 4 or 6. Do not run with really big numbers unless you want your machine to be dog-slow!

Let that compile, and maybe read some more of the [http://lwn.net/Kernel/LDD3/ Linux Device Drivers] book.

Note: when you run make with a .config file that was copied from a different kernel than the one you were building, you may be prompted to make choices about which new kernel features to enable. When in doubt, just choose the default choice. You can do that by hitting enter. A faster way to simply chose all the defaults is to run make menuconfig.

Installing the kernel

To install a kernel, you will need to either manually update your GRUB configuration file, or have an installkernel script. This script installs the kernel to /boot/, installs modules to /lib/modules/X.Y.Z/ (where X.Y.Z is something like 3.1.5), and updates file /boot/grub/grub.conf. Fortunately, Ubuntu provides an installkernel script in /sbin/installkernel. The grubby RPM provides it for RPM based systems.

If you have an installkernel script, you can just run

sudo make modules_install install

Or if you don't have sudo installed, run

su -c "make modules_install install"

Running your kernel

Linux stores both old and new kernel versions, so you can boot into your old kernel if you run into issues with your new kernel. The bootloader program called grub lets you chose which kernel you want to boot into.

The grub bootloader usually presents users with a choice of kernels and you can reboot into a known good kernel if your new compile doesn't work. Some distros (like Ubuntu) use a default grub configuration that hides that menu. You can usually get the menu to appear by mashing the ESC key during boot after the BIOS display disappears.

To make the grub boot menu always appear under Ubuntu, run

sudo vim /etc/default/grub

Then delete these two lines:

GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true

This next line controls how long grub shows the menu before it choses the kernel at the top of the list (which is usually the most recent kernel):

GRUB_TIMEOUT=10

You may want to increase the GRUB_DEFAULT timeout from 10 seconds to 30 seconds or more. I set it to 60 seconds.

After you've finished editing the grub file, you need to tell grub that you made a change, so that can re-write some automatically generated files. Run this command:

sudo update-grub2

You will (usually) need to reboot into your new kernel.

Email software

To send patches, you will need to be able to have a mail transport client installed:

sudo apt-get install esmtp

Now you will be able to send email through git-send-email. However, we also recommend having a mail client installed that can handle plain text patch format. Our recommendation is a text-based email client called mutt:

sudo apt-get install mutt

Optional tools

{{{sudo apt-get install gitk }}}

In the git/kernels/linux/ directory, run {{{make tags }}}

That will make ctags for the source code. When you start editing code in vim from the base directory (git/kernels/linux/), you can use the CTRL+[ to look up the definition of a function. See the [http://vim.wikia.com/wiki/Browsing_programs_with_tags ctags entry] in the vim tips wiki for more info.

Done!

Yay, you're done setting up your kernel development environment! Now go start at [wiki:OPWfirstpatch these directions] to get more instructions for how to modify the Linux kernel and send your first patch.

KernelNewbies: OutreachyfirstpatchSetup (last edited 2013-05-03 18:28:22 by SarahSharp)