RPi - auto start application on boot

There are a number of ways to get a Raspberry Pi to start an application on boot... making it good for IoT type applications...

You could use a cron job (crontab).... or edit the /etc/rc.local file

sudo nano /etc/rc.local

eg. add a line
python myscript.py

Mac OSX - can't use SUDO with some folders anymore in El Capitan - solution

This works - from here -   http://stackoverflow.com/questions/32590053/copying-file-under-root-got-failed-in-os-x-el-capitan-10-11/32590885#32590885 

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El Capitan now protects certain system directories in "rootless" mode (a.k.a. System Integrity Protection). If you run the command ls -lO /System/Library/LaunchDaemons you'll see that the directories and files under there are now marked as "restricted."

You can disable rootless mode like this:

1. Reboot into recovery mode (reboot and hold down Cmd-R)
2. Open a terminal
3. Use this command: csrutil disable
4. Reboot and run the command that worked prior to El Capitan

When you're done, it is highly recommended that you re-enable SIP by following the same steps, but using csrutil enable in step 3.