Locked out of Debian embedded device after mistake in fstab

Question

I am working with an embedded Linux device with Debian 9 installed. The device has an internal storage and the option to extend the storage with a sd card. I want to use the extra sd card for additional storage and I configured it to be mounted at boot in /etc/fstab.

However, after reboot I am unable to access my device. I can ping its IP but my attempst to connect through ssh are refused. The device provides a serial port for debugging to which I have connected using Putty and where I have discovered my mistake in the fstab:

Unrecognized mounting option default or missing value

That is, I have written default instead of defaults in /etc/fstab. Now I am well aware of my mistake but I have no idea of how to solve it. I cannot type anything in the serial port. It says:

You are in emergency mode. After logging in, type "journalctl -x
Cannot open access to console, the root account is locked.
See sulogin(8) man page for more details.

The command prompt mentions the option to enter the BIOS menu at boot by pressing DEL it does not recognize that key being pressed.

I cannot access the internal storage where the fstab is. Removing the extra sd card does not work either because the system searchs for it at boot. The device has a reset button that is not working anymore.

Is anything I can do to access my device?

Answer 1

What is the device ?

Since:

• fstab is faulty.
• your root account is locked.

You won't be able to recover this way. The only way to recover is:

• Entering the bootloader and make your device boot using NFS or directly on the SD-Card (and then your repair the embedded storage). Often, embedded devices use uboot which is an Open Source well documented bootloader that is able to boot using several medium.
• Use a tool provided by your board manufacturer (for example boards from Amlogic can be totally flashed from scratch with USB Burning tool, Android devices can using fastboot or others manufacturer tools like EMMA for sony phones) to totally rework your device.

Answer 2

I have finally been able to update the firmware using an option in the bootloader menu.

I have been able to access the bootloader menu using a different terminal for the serial communication. First I thought that the problem of the DEL key pressing not being recognized was related to the lock of the root account. However, using Tera Term instead of Putty, pressing DEL has been recognized at boot.