Tente se conectar com mysql -u someuser -p -h 127.0.0.1
.
Se você conseguir se conectar sem uma senha, você salvou as credenciais em um .my.cnf ou criou uma conta que permite o acesso sem uma senha.
Esse comentário dos documentos do mysql também pode estar relacionado.
If you cannot figure out why you get Access denied, remove from the user table all entries that have Host values containing wildcards (entries that contain '%' or '_' characters). A very common error is to insert a new entry with Host='%' and User='some_user', thinking that this allows you to specify localhost to connect from the same machine. The reason that this does not work is that the default privileges include an entry with Host='localhost' and User=''. Because that entry has a Host value 'localhost' that is more specific than '%', it is used in preference to the new entry when connecting from localhost! The correct procedure is to insert a second entry with Host='localhost' and User='some_user', or to delete the entry with Host='localhost' and User=''.