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The chown statement in the article uses a period instead of a colon.

Should it be "chown -R mysql:mysql" ?

The period works with GNU coreutils chown (e.g. on Linux), but not other versions.

I think it whines that it's deprecated though.

Yes, it's a good habit to get into because . is allowed in user and group names whereas : can't be; it's the field separator in /etc/{passwd,group}.