Can't log into mysql shell
Please, review my.cnf files (see oficial documentation for file locations https://dev.mysql.com/doc/refman/5.7/en/option-files.html).

Search under the [client] section if exist an entry called socket, i.e:

[client]
port=3306
socket=/tmp/mysql.sock


Replace it with the right path to mysql.sock and try again.
To get the mysql.sock, use ps -FU mysql -H | more and get the --socket value