Executing a script at startup and shutdown in Ubuntu

Command for Startup of Ubuntu
Edit /etc/rc.local and add your commands
The script must be ends with "exit 0"

Command for Rebooting Ubuntu
Put your script in /etc/rc0.d
Make it runable (sudo chmod +x myscript)
The name of your script must begin with K99 and run at the right time.

Command for shutdown Ubuntu
Put your script in /etc/rc6.d
Make it runable (sudo chmod +x myscript)
The name of your script must begin with K99 and run at the right time.