1, init is the system boot up after the first running process, is the system's most important daemon, the process number is always 1.
2. With the boot of the machine, Init starts at run Level 0 and runs from the first level to the default run level set in/etc/inittab. When the machine shuts down, the same process is performed in reverse order.
3. The main file of the startup script is located under/ETC/INIT.D This directory, each script is responsible for a daemon or a specific aspect of the system.
4, in order to achieve different operating levels need to run those scripts (and what parameters, K start stop, s start), when the system entered a new runlevel, not directly in the INIT.D directory, but instead of looking for the RC level. D directory, Level is the level of operation to be entered.
5,/etc/rc.local (rc.local-rc.d/rc.local) script is the last script to run as part of the startup process.
Startup script _ Unix/linux System Management Technical Manual Fourth edition