Question

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How can I start Busybox at boot time, from GRUB, or even before GRUB?

rated 0 times [ 1] [ 0] / answers: 1 / hits: 3688 / 3 Years ago, thu, may 6, 2021, 6:11:10

Most Busybox questions are related to the fact that users are dropped to a Busybox shell due to some unknown issues at boot time. This must make Busybox one of the most hated pieces of software.

My problem is the opposite. I want to deliberately start Busybox at boot time either from GRUB, or even before GRUB. Is this possible? How can I do it? The purpose is to execute some commands before the boot sequence is reinitiated. So basically I want to execute some commands to make some hardware available to the bootloader.

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4 Years ago

answered 3 Years ago irripri · Accepted Answer

You will need to make a custom initrd.

Extract an initrd, note I use ~/initrd as a working directory

cp /boot/initrd_your_version ~

cd ~/initrd

gzip -dc ../initrd_your_version | cpio -imvd --no-absolute-filenames

You did not mention what you wanted to do, so I can only give general advice here.

Now, add any libs and/or binaries you need into the ~/initrd . Use ldd to identify dependencies.

Edit ~/initrd/init , it is a shell script, so add in what you need.

Package it up

cd ~/initrd

find . | cpio --quiet --dereference -o -H newc | gzip -9 > ../initrd-custom.img.your_version

See also: http://en.gentoo-wiki.com/wiki/Initramfs

Sure that link is gentoo, but I do not know of any such detailed document for Ubuntu.

See also : http://www.busybox.net/about.html