With fresh installation of MariaDB 10.4.17 on docker, when we run mysql_upgrade, its getting failed with below error.

mysql.user

Error    : The user specified as a definer ('mariadb.sys'@'localhost') does not exist

error    : Corrupt

Phase 4/7: Running 'mysql_fix_privilege_tables'

ERROR 1449 (HY000) at line 7: The user specified as a definer ('mariadb.sys'@'localhost') does not exist

ERROR 1449 (HY000) at line 16: The user specified as a definer ('mariadb.sys'@'localhost') does not exist

ERROR 1449 (HY000) at line 59: The user specified as a definer ('mariadb.sys'@'localhost') does not exist

..

You can reproduce it on docker with simple steps.

Step 1: docker run -d --name marianil -eMARIADB_ROOT_PASSWORD=nil2020 -P mariadb/server:10.4
Step 2: docker start marianil
marianil
Step 3: echo "show databases" | docker exec -i marianil mysql --user=root --password=nil2020 – confirm is instance is running or not.
Database
information_schema
mysql
performance_schema
[root@localhost mysql]# echo "select version()" | docker exec -i marianil mysql --user=root --password=nil2020
version()
10.4.17-MariaDB-1:10.4.17+maria~bionic
[root@localhost mysql]#

Step 4: docker exec -i marianil mysql_upgrade --user=root --password=nil2020