Docker Cookbook

1.17 Backing Up a Database Running in a Container | 31

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Discussion
Although this recipe uses MySQL, the same techniques are valid for Postgres and
other databases. If you use the 
Postgres
 image from Docker Hub, you can also see in
the 
Dockerfile
 that a volume is created (
VOLUME /var/lib/postgresql/data
).
1.18 Sharing Data in Your Docker Host with Containers
Problem
You have data on your host that you would like to make available in a container.
Solution
Use the 
-v
option of 
docker run
to mount a host volume into a container.
For example, to share the working directory of your host within a 
/cookbook
directory
in a container, do this:
$ ls
data
$ docker run -ti -v "$PWD":/cookbook ubuntu:14.04 /bin/bash
root@11769701f6f7:/# ls /cookbook
data
In this example, you mount the working directory in the host into the 
/cookbook
directory in the container. If you create files or directories within the container, the
changes will be written directly to the host working directory, as shown here:
$ docker run -ti -v "$PWD":/cookbook ubuntu:14.04 /bin/bash
root@44d71a605b5b:/# touch /cookbook/foobar
root@44d71a605b5b:/# exit
exit
$ ls -l foobar
-rw-r--r-- 1 root root 0 Mar 11 11:42 foobar
By default, Docker mounts the volume in read-write mode. If you want to mount it in
read-only mode, you can specify it after the name of the volume, using a colon. For
example, to mount the previous working directory to 
/cookbook
as read-only, you
would use 
-v "$PWD":/cookbook:ro
. You can inspect your mount mapping with the
docker inspect
 command. See 
Recipe 9.1
 for more information about 
inspect
.
$ docker inspect -f {{.Mounts}} 44d71a605b5b
[{ /Users/sebastiengoasguen/Desktop /cookbook true}]