1) Reset Linux password by booting from Linux Mint 19.3 ISO image then change the following line in /boot/grub/grub.cfg:

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linux /boot/vmlinuz-[kernel version]-generic root=UUID=[letters and numbers]\[letters and numbers] ro quiet splash $vt_handoff
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2) Change "ro quiet splash $vt_handoff" to "rw init=/bin/bash" so it now reads:

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linux /boot/vmlinuz-[kernel version]-generic root=UUID=[letters and numbers]\[letters and numbers] rw init=/bin/bash
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3) Press F10 to boot your system. System will boot up to a passwordless root shell.


4) Type in passwd yourusername (literally use "passwd" but not "yourusername"). If you forgot username, type cat /etc/passwd first to get a list of all users, which should appear at the end. Set your new password.


5) Restart your system.