How to Autorun application at the start up in BeagleBone

I am using BBB with latest debian version 9.2.I want Autorun application at the start up.
firstly i am trying to crontab & systemd service it’s working but not showing debugged data on serial debug.

A basic method I use is to run things from /etc/rc.local. Any program
called from /etc/rc.local will get run at system startup.

/etc/rc.local directory not available
also write script file in rc5d ,rc3.d directory but not working.
need a help!!!

crontab log can be specified if your /etc/rc.local is not existent or executed.

depend on you linux distro also have a look like /etc/init.d/

dogtag:[ Debian Image 2018-01-07]
bootloader:[microSD-(push-button)]:[/dev/mmcblk0]:[U-Boot 2018.01-rc3-00002-gb33224]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot 2017.09-00002-g0f3f1c7907]

on crontab working but output not showing on serial debug.

/etc/rc.local directory not available

It's a file, not a directory. Just try it:

echo touch /tmp/testRClocal > /etc/rc.local

and reboot the system. You should see the newly created file
/tmp/testRClocal when you login into the running system.

also write script file in rc5d ,rc3.d directory but not working.

What did you write into those files? which OS version are you running?
Need more detail to help you.
Most new systems use systemd rather than the old SysV /etc/rc* files,
so this may not work (but /etc/rc.local is actually emulated by
systemd so that should be OK).