MySQL docker 5.7.6 and later fails to initialize database

[guss77]

When using the docker image to start without an existing database, the container's entrypoint.sh script tries to call the mysqld binary to create the database. This fails in versions later than 5.7.5 because the script starts by calling mysqld --verbose --help to get the configured datadir and when that runs and there is no database, it initializes it automatically.

When the script then calls --initialize, that fails with the error:

 [ERROR] --initialize specified but the data directory has files in it. Aborting.

The workaround is to run mysql:5.7.5 to create the database, then upgrade to a later image, which will work because the database already exists.

[md5]

The mysql:5.7.6 image was tested with this test before release: https://github.com/docker-library/official-images/blob/master/test/tests/mysql-basics/run.sh

You may need to provide some more information about your failure.

[guss77]

The problem is one of permissions: the container has the data dir /var/lib/mysql owned by root, so when entrypoint.sh is calling mysqld --help to get the data dir, the directory isn't writable by mysqld and mysqld can't write the innodb log files it will normally create automatically when there is no database already set up. entrypoint.sh will later chown the directory.

The problem is that the container relies on this behavior for successful initialization, but it can break when using a volume to mount the data dir from another long-running file system (whether on the host or another container): when a the container is started on an empty volume, the mysql user may have write permissions there (because the volume is writable to anyone or because the volume was previously used to host another mysql database and the admin just rm -rf $vol/* it). If that is the case, then the first call to mysqld --help will create the innodb log files and then initialization will fail.

[ltangvald]

This is a known issue with MySQL 5.7.6 and later, and is being looked into:
http://bugs.mysql.com/bug.php?id=75995.
We have a temporary workaround in the mysql/mysql-server:5.7 image:
https://github.com/mysql/mysql-docker/blob/mysql-server/5.7/docker-entrypoint.sh
Note that the whole if-file-exists check can probably be replaced with a simple rm -f

[ltangvald]

There's a better workaround for this; running mysqld --verbose --help with the --innodb-read-only option prevents it from creating the files. Could maybe make a PR for this, as it's not as ugly :)

[tianon]

👍 🤘

It's not necessary in our latest version though, is it? Are we still creating those files prematurely?

[ltangvald]

The reason it's not necessary is that mysqld doesn't have write access to /var/lib/mysql on the Debian image (permissions on $DATADIR are set after --verbose --help is run), so it'll simply fail to create the files. On the OL image ownership on the folder is set when the server is installed, so this workaround is needed even with the default setup.

The problem for the official image is that if the user provides a --datadir that is writable from the start, it'll create the files and initialization will fail.

[yosifkit]

@guss77 did #78 fix this for you?

[bittner]

Disclaimer

Not sure if I will be threatened to death for saying this, but ... well, see below.

ℹ️ This is meant as a help for people looking for a solution for their project, not for this project.

Use MariaDB

Instead of using the mysql image people may use the mariadb image, which works flawlessly with Docker volumes. Example docker-compose.yml file:

version: "2"

volumes:
  db_data: {}

services:
  app:
    # ...
    depends_on:
      - db

  db:
    image: mariadb
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: mysql
      MYSQL_USER: mysql
      MYSQL_PASSWORD: mysql
    volumes:
      - db_data:/var/lib/mysql/data

[ltangvald]

The MySQL and MariaDB images are for the most part maintained by the same people and process, one working as well as the other (or as badly). This bug is for MySQL 5.7, which doesn't have a comparable MariaDB version.