Mysql-server e phpmyadmin recem instalado não entra com root (debian 9.5)

Problemas com acesso root no phpmyadmin

Comandos executados estão em vermelhos

root@lab-pc2:/home/usuario# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.7.26-0ubuntu0.18.04.1 (Ubuntu)

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Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('nova-senha');
Query OK, 0 rows affected, 2 warnings (0.13 sec)

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> update user set plugin = '' where user = 'root';
Query OK, 1 row affected (0.10 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.06 sec)

mysql> exit
Bye
root@lab-pc2:/home/usuario#