Unable to mount docker folder into host using docker-compose

Question

Here I created docker container which use the mariadb image and created three volumes as below.

docker-compose.yml

version: '2.0'

services:
  mariadb:
  image: mariadb:latest
  restart: always
  container_name: mariadb
  environment:
    - MYSQL_ROOT_PASSWORD=root
    - MYSQL_DATABASE=testdb
  ports:
   - 3307:3306
  volumes:
   - ./database:/var/lib/mysql
   - ./_conf/mariadb.cnf:/etc/mysql/my.cnf:ro
   - ./logs:/var/log/mysql

First two volume works successfully but I can't able to find mariadb-logs files into logs folder. I seems logs folder showing blank on host as well as on container(/var/log/mysql). I think host folder override into docker file system.

If I remove this volume(./logs:/var/log/mysql) from docker-compose then logs files are showing on container.

My plan is to mount /var/log/mysql/ folder to local machine.

Thanks !

Answer 1

If you use CentOS 7 (as I have ). You may have SELinux turned on by default.check https://www.rootusers.com/how-to-enable-or-disable-selinux-in-centos-rhel-7/ or mount like this:

  volumes:
   - ./database:/var/lib/mysql:Z
   - ./_conf/mariadb.cnf:/etc/mysql/my.cnf:Z
   - ./logs:/var/log/mysql:Z

Answer 2

If you're running a RedHat-based distribution e.g. Fedora or CentOS, you may have SELinux turned on by default. You can automatically permit your containers to access files on the hosts by mounting with the :Z option, like so:

  volumes:
   - ./database:/var/lib/mysql:Z
   - ./_conf/mariadb.cnf:/etc/mysql/my.cnf:Z
   - ./logs:/var/log/mysql:Z

Answer 3

If /var/log/mysql:/var/log/mysql is defined as a volume then the content that reside in the container's /var/log/mysql/ will be stored in the /var/log/mysql/ folder on the host.

It could be possible that it is not possible to mount the /var/lib/mysql as SElinux or app armor is preventing this.

https://hub.docker.com/_/mysql/

Note that users on host systems with SELinux enabled may see issues with this. The current workaround is to assign the relevant SELinux policy type to the new data directory so that the container will be allowed to access it:

$ chcon -Rt svirt_sandbox_file_t /my/own/datadir