My issue and fix: my /var/lib/mysql is in another location and the /var/lib/mysql is a softlink.
delete /var/lib/mysql-upgrade/DATADIR.link before doing the upgrade and then I had no issue upgrading to 5.7
My issue and fix: my /var/lib/mysql is in another location and the /var/lib/mysql is a softlink.
delete /var/lib/ mysql-upgrade/ DATADIR. link before doing the upgrade and then I had no issue upgrading to 5.7