Essential command binaries that need to be available in single user mode, e.g. cat, ls, cp
knerels, initrd
essential devices like hard drives and printers, also /dev/null lives here
Host-specific system-wide configuration files (the name comes from et cetera). /etc/init.d/ contains services for starting and stopping mysql and apache.
users' home directories
log files
Information about the running system since last boot, e.g., currently logged-in users and running daemons.