Difference between passwd and passwd- file [duplicate]

Difference between passwd and passwd- file [duplicate]

/etc/passwd- is a backup of /etc/passwd maintained by some tools, see the man page. There's also a /etc/shadow- usually, for the same purpose.

So, by observing the output of the command diff /etc/passwd{,-} in your question, nothing seems fishy. Someone (or something) changed the name of your mysql user.