The 'init=/bin/bash' has to be appended at the bot time. This is when the bootloader loads, when you have the grub screen with all the boot options.
In case this is not possible boot with a live cd - or boot with debain with rescue mode - and edit the /etc/passwd and delete the charaters ':0:0:' after the root entry (be careful that is our root password. You would next nned to delete the encrypted password from '/etc/shadow' after the root: entry (this is the encrypted password). The root password would then be blank.
I just thought of an easier way, boot with a live cd go to /etc/sudoers and uncomment the last line (works for slackware) and then you can log in as yourself and just run sudo, that should do it.
MAKE A BACKUP OFF THE FILES YOU EDIT. MAKE SURE THAT THE BACK UPS ARE VERIFIED.
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