The /sbin/rcS script runs the /etc/rcS.d scripts to bring the system up to run level S. The following tasks are performed by these scripts:
Establishes a minimal network
Mounts /usr, if necessary
Sets the system name
Checks the root (/) and /usr file systems
Mounts pseudo file systems (/proc and /dev/fd)
Rebuilds the device entries for reconfiguration boots
Checks and mounts other file systems to be mounted in single-user level