Dear Mahendra Dobariya,
In message BAY176-W171CCC856593BA0F7380DC90240@phx.gbl you wrote:
hello,,I am from India.I am electronics hobbyist.currently I am using beaglebone black in my project.and I am afraid of security of linux systemits quite easy to copy or modify data from linux system if it has physical access.lets say ,I have BBB , and I boot it from external device(like external mmc ). and mount internal emmc then modify shadow file. and then boot from internal Emmc. now I will get root access , and I can modify anything on the system.
If you cannot prevent physical access, you cannot prevent one from taking full control over your hardware. If needed, I'll attach a JTAG debugger and run my own version of U-Boot that circumvents all security measures you installed in yours.
Best regards,
Wolfgang Denk