It looks like it has something to do with having no password for the root user like on my dev box.
I have the same [ERROR] 1396 Operation ALTER USER failed for 'root'@'localhost' in my error log and after every try a stale *.tmp file in /var/lib /mysql-files. The "ALTER user" command comes from the file "/var/lib/dpkg/info/mysql-server-5.7.postinst" You read in line 368: "If there is no root password set we enable the auth_socket plugin for the root user." This seems fails for some SSL related problems. I could solve the block with these steps: 1. delete stale tmp files in /var/lib/mysql-files 2. Comment the line 370 which is : echo "ALTER USER 'root'@'localhost' IDENTIFIED WITH 'auth_socket';" >> "$initfile" -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1817374 Title: mysql-server-5.7 5.7.25 upgrade did not complete properly To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1817374/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs