How to run a script during boot as root

I had a script that automatically enables my wifi without using networkmanager, but I don't know how to run the script as root while the system is booting. How do I make the script run automatically during boot?

Place the script you want to run in the /etc/init.d directory and make the script executable.

chmod 755 myscript

Once that is done create a symbolic link in the run level directory you would like to use, for example if you wanted to run a program in the graphical runlevel 2, the default runlevel for Ubuntu, you would place it in the /etc/rc2.d directory. You just cannot place it the directory, you must signify when it will run by indicating the startup with an “S” and the execution order is important. Place it after everything else that is in the directory by giving it a higher number.

If the last script to be run is rc.local and it is named S99rc.local then you need to add your script as S99myscript.

ln -s /etc/init.d/myscript /etc/rc3.d/S99myscript

Each backward compatible /etc/rc*.d directory has symbolic links to the /etc/init.d/ directory.

Use a crontab option to make your script run after reboot,

you can do it by adding @reboot code in cron

Open crontab by root user:

$ sudo crontab -e

Add the next record at the bottom:

@reboot yourScriptPath 

That will do what you want.