"The results you get can fall short of your expectations if you
don't also reorder the boot sequence. And if you have installed
readahead, you may even have unpleasant surprises... ,p>"When
you install readahead, it places an init script in /etc/init.d and
its symbolic link /etc/rcS.d/S02readahead. As long as the scripts
in /etc/rc?.d directories are executed in lexicographic order, this
script is executed after S02mountkernfs. This is fine, because
readahead actually depends on /proc being mounted, which is exactly
what mountkernfs does.
"But what happens when, as a consequence of CONCURRENCY=shell,
all scripts with the same priority are run in parallel? Then
readahead and mountkernfs, both with priority 02, are launched
together, and the latter may or may not mount /proc before the
former requires it."