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I used docker commit and now the container won't run properly. Should I:

  • specify a new data folder within the container, so it will get deleted when I delete the container
  • delete the host folder contents under /var/lib/mysql?

What I did was I started a Docker container:

docker run -p 33069:3306 --name some-mysql -e MYSQL_ROOT_PASSWORD=test -d mysql:8.0.26 mysqld --default-authentication-plugin=mysql_native_password

Configured some stuff like remote root login, inserted some data into it. Then I wanted to back it up and did:

docker commit -p 6b836bfdf062 backup-mysql8

Which went OK:

root@server:/home/user# docker images | grep mysql
backup-mysql8                                             latest                1effec593a03   45 minutes ago   514MB

Then I stopped and removed the old container. And tried to start a new one from the backup:

docker run -p 33069:3306 --name some-mysql -e MYSQL_ROOT_PASSWORD=test -d mysql:8.0.26 mysqld --default-authentication-plugin=mysql_native_password -d backup-mysql8

After a few seconds, it would just die.

root@server:/var/lib/mysql# docker ps -a
CONTAINER ID   IMAGE                                                                 COMMAND                  CREATED          STATUS                      PORTS                                                                                  NAMES
13b17d3af8f7   mysql:8.0.26                                                          "docker-entrypoint.s…"   21 minutes ago   Exited (1) 21 minutes ago                                                                                          some-mysql

I looked at the logs:

docker logs 13b17d3af8f7

And found this:

2021-09-10T15:15:37.074480Z 0 [ERROR] [MY-013236] [Server] The designated data directory /var/lib/mysql/ is unusable. You can remove all files that the server added to it.

I used inspect and saw that this new host is using my host folder /var/lib/mysql, is that what this means?

docker inspect 13b17d3af8f7

docker using local host /var/lib/mysql

The problem is that that folder on my host machine is already being used and I don't think it's used by the previous container.

root@server:/var/lib/mysql# ls -l
total 110652
-rw-r----- 1 mysql mysql       56 feb 13  2020 auto.cnf
-rw------- 1 mysql mysql     1676 feb 13  2020 ca-key.pem
-rw-r--r-- 1 mysql mysql     1112 feb 13  2020 ca.pem
-rw-r--r-- 1 mysql mysql     1112 feb 13  2020 client-cert.pem
-rw------- 1 mysql mysql     1680 feb 13  2020 client-key.pem
-rw-r--r-- 1 mysql mysql        0 iul 28 06:01 debian-5.7.flag
-rw-r----- 1 mysql mysql      291 feb 13  2020 ib_buffer_pool
-rw-r----- 1 mysql mysql 12582912 feb 13  2020 ibdata1
-rw-r----- 1 mysql mysql 50331648 feb 13  2020 ib_logfile0
-rw-r----- 1 mysql mysql 50331648 feb 13  2020 ib_logfile1
drwxr-x--- 2 mysql mysql     4096 feb 13  2020 mysql
drwxr-x--- 2 mysql mysql     4096 feb 13  2020 performance_schema
-rw------- 1 mysql mysql     1680 feb 13  2020 private_key.pem
-rw-r--r-- 1 mysql mysql      452 feb 13  2020 public_key.pem
-rw-r--r-- 1 mysql mysql     1112 feb 13  2020 server-cert.pem
-rw------- 1 mysql mysql     1676 feb 13  2020 server-key.pem
drwxr-x--- 2 mysql mysql    12288 feb 13  2020 sys

What and how to do it?

Buffalo
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    You probably don't ever want to use `docker commit`. In this particular case, [docker commit mysql doesn't save](https://stackoverflow.com/questions/37947863/docker-commit-mysql-doesnt-save) because the data is always in a volume. More generally there is some discussion on [How can I backup a Docker-container with its data-volumes?](https://stackoverflow.com/questions/26331651/how-can-i-backup-a-docker-container-with-its-data-volumes). But `docker commit` isn't part of a reproducible work flow. – David Maze Sep 10 '21 at 18:31
  • I don't care about the data. I'm asking why a new container won't start using the old container's volume. – Buffalo Sep 13 '21 at 07:47

1 Answers1

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if you need persistent data stored, you should map /var/lib/mysql to a host folder instead.

e.g.

docker run -p 33069:3306 --name some-mysql -v ./mydata:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=test -d mysql:8.0.26 mysqld --default-authentication-plugin=mysql_native_password

Update: docker inspect output just represent the section VOLUME ["/var/lib/mysql"] in Dockerfile.

Ronald Poon
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