In this post I build a custom embedded Linux bootable CD that I can run in an x86 VM. I would like to appreciate the help I received from the official documentation.
Get buildroot. I use version 2011.02 in this post. My build machine is a Virtual Box VM running Ubuntu 10.04 LTS. I have Virtual Box Guest Additions installed, which I use to access a shared folder on the host OS, to get files in and out of the VM (I could probably use a raft of different things to do this but I find this setup painless).
To configure buildroot you require several tools to be present,
make is one, but most Linux installations have that already. You’ll probably need to
apt-get a few things along the way. You’ll will certainly require
ncurses, which can be obtained as follows:
sudo apt-get install libncurses5-dev
To configure buildroot you need run
make menuconfig in the folder you extracted it. Here’re the options I use:
- Target architecture – i386
- Target architecture variant – i686
- Kernel – Kernel version: 18.104.22.168, Kernel configuration: Using a defconfig, Defconfig name: i386
- Target filesystem options – ext2, iso image
- Bootloaders – grub
Exit and choose to save the configuration file.
make once you are done saving the buildroot configuration. The build process takes some time because it downloads lots of different things required to build the toolchain, Linux kernel, and the root filesystem. Go and have some coffee. You can speed up the build process by setting up the Virtual Box VM to use multiple cores on the host PC, and allowing buildroot to run as many jobs as you have cores (default setting is 2). This is done using
make menuconfig at Build Options, Number of jobs to run simultaneously. Using multiple cores can be buggy, I have had my VM freeze several time, so use it sparingly.
Run embedded Linux
Copy the iso file
rootfs.iso9660 from the
output/images folder to the host machine as
rootfs.iso. Create a new Virtual Box VM and set the iso file as the CD/DVD drive. Start the new VM. If all goes well (it won’t) you’ll get the login prompt where just typing
root should let you in to the command line. This first time you’ll not be able to get in because we did not configure the Linux kernel for the
ext2 filesystem. Let us see how to do that now.
Configure the Linux kernel
You have built once and all kernel sources should be available at the folder
output/build/linux-22.214.171.124. The kernel build configuration file
.config is located in that folder. To change that configuration we’ll need to do two things – modify the linux configuration using
make linux-menuconfig, and modify the buildroot configuration for the kernel to use that configuration file during the build.
To modify the Linux configuration, invoke
make linux-menuconfig from the buildroot root folder. Head over to File systems and select Second extended fs support. Exit and save the configuration.
To modify the buildroot configuration to use the new kernel configuration, execute
make menuconfig. Head over to Kernel, Kernel configuration, and select Using a custom config file. Change Configuration file path to
output/build/linux-126.96.36.199/.config. Exit and save the buildroot configuration. Build, copy the resulting iso file to the host OS and run the test VM. You should now be able to log in as root.
Now, you can modify your custom embedded Linux kernel to support other devices you’ll need, deploy it to hardware… sky’s the limit!
Kudos: Fabio Urquiza at cesar.org.br