Why do you need to un-mount it ? Try < -f > flag, for force.
Hey! maybe there is a work-around?...
Perhaps I should describe the goal? That always seems to help.
The motivation for chroot'ing is that I am not familiar with another way
to run mkinitrd. Honestly, I am surprised there is not -root option such
as with the rpm command or tar's -C, etc. If I could specify my root
file system on the command line then I would not need to chroot to
So, to answer your question, the reason I believe I need to unmount, is
because after chroot exits, I archive the entire file system with tar.
If I do not unmount, tar complains with errors that the file system is
mounted or some such message. I can set up the situation again and
fetch the exact error message.
Through experience, I know that if I unmount properly, I avoid the
tar error when creating the tar archive.