Can't change login pw

Ubuntu MATE 18.04 LTS. Have forgotten my login PW so have attempted to change it following these directions https://itsfoss.com/how-to-hack-ubuntu-password/

Boot into recovery mode
Get into shell prompt
$ mount -rw -o remount /
$ passwd jim
$ new password
$ new password
$ exit
Then booted normally. However it didn't work. My new pw that is.

Am I at least correct in assuming my username is correct?

What should I try next? Any feedback welcome!
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