Why does docker prompt “Permission denied” when backing up the data volume?

Question

I am following the docker document to test the backup process of data volumes.

The following 2 steps are all OK:

docker create -v /dbdata --name          


        

Answer 1

I just tried the commands you listed and they worked for me, both under an OSX platform and also a straight up linux platform. The thing is you are mounting $(pwd) (from your host) to /backup (in the ubuntu image, third docker run above).

I suspect that when you launch the command you are in a directory that is not writable? I tried to get it to fail like this:

mkdir failme
chmod 000 failme
cd failme
docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata

But, it worked :-)

So, I cd'ed into a directory that isn't writable by root:

cd /proc
root@kube:/proc# docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
tar: /backup/backup.tar: Cannot open: Permission denied
tar: Error is not recoverable: exiting now

Is it possible that you are starting from a directory that is not writable by root?

Please post the output to these commands: First, run:

docker run --name ins --volumes-from dbdata -v $(pwd):/backup ubuntu sleep 99999 &

(instead of the backup command command you have listed.)

then do an inspect and post those results:

docker inspect ins

And the answer turned out to be that it was the selinux causing the errors. The Original Poster found the answer:

setenforce 0