The rc0 script contains run commands that enable a smooth shutdown and bring the system to a single-user state; run levels 0 and s. In addition to commands listed in within the script itself, rc0 contains instructions to run commands found in the /sbin/rc0.d directory. The script defines the conditions under which the commands execute; some commands run if the system is being shut down while others run if the system is being shut down and rebooted to single user.
By convention, files in the /sbin/rc0.d directory begin with either the letter "K" or the letter "S" and are followed by a two-digit number and a filename, for example: K00enlogin K05lpd K60cron K30nfs
In general, the system starts commands that begin with the letter "S" and stops commands that begin with the letter "K." The numbering of commands in the /sbin/rc0.d directory is important since the numbers are sorted and the commands are run in ascending order. Files in the /sbin/rc0.d directory are normally links to files in the /etc/init.d directory.
An entry in the inittab file causes the system to execute the rc0 script, for example: ss:Ss:wait:/sbin/rc0 shutdown < /dev/console > /dev/console 2>&1 s0:0:wait:/sbin/rc0 off < /dev/console > /dev/console 2>&1
The following operations are typical of those that result from executing the rc0 script and the commands located in the /sbin/rc0.d directory: Notify users that the system is shutting down. Sync the disks Stop system services and daemons Stop processes Kill processes Unmount file systems Invoke init if the system is being shut down to single user
The killall command sends a SIGTERM signal to stop running processes; SIGKILL follows to kill all processes except the process which initiated the call. The umount -a command unmounts all file systems except the root file system.
Commands: init(8), killall(8), rc2(8), rc3(8), shutdown(8) delim off