bzImage, root device Q

From: D. Stimits (
Date: Fri Jul 20 2001 - 02:41:31 EST

When booting to a bzImage kernel, bytes 508 and 509 can be used to name
the minor and major number of the intended root device (although it can
be overridden with a command line parameter). Other characteristics are
also available this way, through bytes in the kernel. rdev makes a
convenient way to hex edit those bytes.

What I'm more curious about is how does the kernel know what filesystem
_type_ the root is? Are there similar bytes in the bzImage, and can rdev
change this? And is there a command line syntax to allow specifying
filesystem type (e.g., something like "vmlinuz root=/dev/scd0,iso9660"
or "vmlinuz root=/dev/scd0,xfs")? Or is this limited in some way,
requiring mount on one or a few known filesystem types ("linux native"
subset comes to mind), followed by a chroot or pivot_root style command
(which in turn means no direct root mount of some filesystem types)?

D. Stimits,
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This archive was generated by hypermail 2b29 : Mon Jul 23 2001 - 21:00:13 EST