Setting MYSQL_USER=root prevents docker-entrypoint-initdb.d scripts from running

[janvogt]

Description

When configuring the official MariaDB container with MYSQL_USER=root, scripts placed in the /docker-entrypoint-initdb.d/ directory are not executed during container initialization. This prevents database creation and other initialization tasks from completing.

Environment

• MariaDB container version: latest
• Docker Compose

Steps to Reproduce

1. Create a docker-compose.yml file:

mariadb:
  image: mariadb:latest
  volumes:
    - wordpress_database_data:/var/lib/mysql
    - ./create_other_wordpress_db.sql:/docker-entrypoint-initdb.d/create_other_wordpress_db.sql:ro
  environment:
    - MYSQL_ROOT_PASSWORD=password
    - MYSQL_USER=root
    - MYSQL_PASSWORD=password
  restart: always

volumes:
  wordpress_database_data:

2. Create an initialization SQL file (create_other_wordpress_db.sql):

CREATE DATABASE IF NOT EXISTS `wordpress`;
CREATE DATABASE IF NOT EXISTS `other_wordpress`;

3. Start the container using docker-compose up

Expected Behavior

Both databases (wordpress and other_wordpress) should be created as specified in the initialization script.

Actual Behavior

The initialization script is not executed and the databases are not created. The container logs show:

mariadb-1  | 2025-03-17 10:00:41+00:00 [Note] [Entrypoint]: Creating user root
mariadb-1  | 2025-03-17 10:00:41+00:00 [Note] [Entrypoint]: Securing system users (equivalent to running mysql_secure_installation)
mariadb-1  | --------------
mariadb-1  | CREATE USER 'root'@'%' IDENTIFIED BY 'password'
mariadb-1  | --------------
mariadb-1  | 
mariadb-1  | ERROR 1396 (HY000) at line 29: Operation CREATE USER failed for 'root'@'%'

Workaround

Changing MYSQL_USER=root to another username (e.g., MYSQL_USER=db_user) allows the initialization scripts to run properly.

Root Cause Analysis

The issue appears to be in the docker_setup_db function within docker-entrypoint.sh. When MYSQL_USER is set to "root", the script attempts to create a user that already exists, causing an error and preventing subsequent execution of initialization scripts.

Additional Information

This behavior significantly impacts containerized applications that rely on MariaDB initialization scripts for setup.

[grooverdan]

omitting MYSQL_USER/MYSQL_PASSWORD as a env variables will also work right? Why is specifying the root user and password twice a desirable configuration?

[yosifkit]

@grooverdan, not sure if it is wanted in the MariaDB image, but docker-library/mysql#749 is what we did in the MySQL image to prevent users from having partially initialized databases* for MYSQL_USER=root and other similar mistakes.

* if they use something that auto-restarts the container without watching the exit code

[grooverdan]

I do like the result of pushing errors rather than silently failing on docker-entrypoint-initdb.d scripts.

[janvogt]

omitting MYSQL_USER/MYSQL_PASSWORD as a env variables will also work right? Why is specifying the root user and password twice a desirable configuration?

Yes, that might very well be. The problem turned up during a hackathon. The project isn't mine, I just wanted to add a second database to a larger docker compose setup multiple people were working on. Took me a couple of hours to find out why the initdb script was not executed. That's why I wanted to share my research.

I do not know if this is best addressed with a documentation change, better error handling, an actual fix, any combination of the above or nothing at all. Just wanted to share my research of what was - at least for me - unexpected behaviour.

Tl;dr: The MYSQL_USER, MYSQL_PASSWORD setting where part of a working project setup, i.e. despite the quoted error, the database was working. So I initially didn't assumed the error to be a factor in the non-execution of my newly added initdb file.