docker cp a folder with a relative symlink: invalid symlink

Question

In my container, I have a folder that contains a relative symlink to a parent's parent subfolder:

$ docker run --name symlink-test ubuntu bash -c "mkdir -p /1/2; touch /1/2/a; ln -s ../../usr /1/2; touch /1/2/z; ls -l /1/2"                                               :(
total 4
-rw-r--r--. 1 root root 0 Mar  4 03:37 a
lrwxrwxrwx. 1 root root 9 Mar  4 03:37 usr -> ../../usr
-rw-r--r--. 1 root root 0 Mar  4 03:37 z

I want to copy the folder /1 to the host. However, I always get the following error:

$ docker cp symlink-test:/1/2
invalid symlink "/tmp/2/usr" -> "../../usr"
$ ls 2
a

Copying the files fails and docker cp aborts after it sees the symlink.

There are some Docker bugs related to this, but they are either fixed or were caused by something different:

• FATA[0000] invalid symlink when copying a symlink with relative parent paths
• Error attempting to cp directory containing symlink

I'm running Docker 1.10.2 on Fedora 23.

Is the above behavior of docker cp intended or is it a bug? If it is intended, what's the reasoning behind it?

Ouzo

What is the current WORKDIR in your container, when you are doing your docker cp? – Retaliation

The current WORKDIR is the default WORKDIR of the Ubuntu image, which is /. – Ouzo

Answer 1

In my case, I get it to work by:

docker cp -L container:/path/to/file.png current/directory/file.png

Cupcake

In the docs, '-L' is described as -L, --follow-link Always follow symbol link in SRC_PATH – Aggi

Answer 2

I don't know whether this behavior is intentional, but here's a workaround:

docker cp my-container:/path/to/dir - | tar -x

Hepplewhite

Answer 3

You could docker exec -it <container> sh then find the symlink of the file you want to copy readlink -f symlinkName and then docker cp that one instead.

Morph

Thanks for the hint, but this doesn't answer the question. – Ouzo

Answer 4

The "docker cp -L " will fail on relative symlinks, you should fix them to be full path instead.

e.g. invalid symlink "/tmp/2/usr" -> "../../usr" usr is a relative symlink to ../../usr. instead change it to: usr -> /full/path/to/usr/

another example: invalid symlink "/working_folder/XXX/lib" -> "../../lib"

because: lib -> ../../lib/ fixed it: lib -> /full/path/to/lib/

and it will work by: docker cp -L /full/path/to/working_folder:/working_folder/

Sakai