document updated 16 years ago, on Nov 6, 2008

Debugging initrd/initramfs images when they don't work correctly.

First of all, you can usually extract the files on a functioning OS.

linux/Documentation/initrd.txt, see "noinitrd". (though how exactly is this used for debugging?)

Some initrd scripts can have special triggers built in to them:

For things built with mkinitramfs, you can specify "debug=vc" as a boot parameter, this outputs stuff to /tmp/initramfs.debug.
(Knoppix) Boot parameter of "BOOT_IMAGE=debug" will open a prompt during initrd.
(Puppy Linux) Boot parameter of "LOGLEVEL=7" will output a bunch of stuff to /tmp/bootkernel.log, /initrd/tmp/bootinit.log, /tmp/sysinit.log, /tmp/xerrs.log, and /var/log/messages.

A nice cpio+qemu script can be created that allows you to rapidly make changes and then test them.

To recreate/update the initrd with your new files:

(background) Tools that create initrd filesystems:

(background) Useful /proc/ stuff.

/proc/cmdline — the boot parameters
/proc/partitions — complete list of disk devices (eg. /dev/sda1 /dev/sda2 ...)