/etc/rc.boot - directory for local or per-package boot scripts.
The /etc/rc.boot directory is obsolete. It has been
superseded by the /etc/rcS.d directory. At boot time, first
the /etc/rcS.d directory is scanned and then, for backwards
compatibility, the /etc/rc.boot directory.
The directory /etc/rc.boot is scanned by the program
run-parts(8). The scripts found that have valid
filenames for the run-parts program will be run in
lexical sort order of the filenames.