Erreur 1044

[mr globule]

Bonjour à toutes et à tous,
Je viens solliciter votre aide sur une technoq ue je ne paitrise pas (encore ^^)
Le serveur est un debian 8.6 et MySQL 5.5 est installé dessus.
J'ai tenté de faire un mysqldump au travers de l'outil backup-manager; mais j'obtiens ce message d'erreur:
mysqldump: Got error: 1044: Access denied for user 'backup'@'localhost' to database 'information_schema' when using LOCK TABLES

Ce qui me surprends car quand j'interroge les droits de cet utilisateur j'ai bien les droits sur localhost suivants:
+-----------+--------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+------------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+-----------------------+-----------------------+
| Host | User | Password | Select_priv | Insert_priv | Update_priv | Delete_priv | Create_priv | Drop_priv | Reload_priv | Shutdown_priv | Process_priv | File_priv | Grant_priv | References_priv | Index_priv | Alter_priv | Show_db_priv | Super_priv | Create_tmp_table_priv | Lock_tables_priv | Execute_priv | Repl_slave_priv | Repl_client_priv | Create_view_priv | Show_view_priv | Create_routine_priv | Alter_routine_priv | Create_user_priv | Event_priv | Trigger_priv | Create_tablespace_priv | ssl_type | ssl_cipher | x509_issuer | x509_subject | max_questions | max_updates | max_connections | max_user_connections | plugin | authentication_string |
+-----------+--------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+------------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+-----------------------+-----------------------+
| localhost | backup | *FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF | Y | N | N | N | N | N | N | N | N | Y | N | N | Y | N | Y | N | Y | Y | Y | Y | Y | Y | Y | N | N | N | Y | N | N | | | | | 0 | 0 | 0 | 0 | mysql_native_password | |
+-----------+--------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+------------------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+-----------------------+-----------------------+
1 row in set (0.00 sec)

Où me suis-je palnté?
D'avance merci de l'aide que vous pourrez me fournir.