Can I change owner of directory that is mounted on

问题:

I'm trying to launch postgres in IBM containers. I have just created volume by:

$ cf ic volume create pgdata

Then mount it:

$ cf ic run --volume pgdata:/var/pgsql -p 22 registry.ng.bluemix.net/ruimo/pgsql944-cli

After logging into container through ssh, I found the mounted directory is owned by root:

drwxr-xr-x  3 root root   4096 Jul  8 08:20 pgsql

Since postgres does not permit to run by root, I want to change the owner of this directory. But I cannot change the owner of this directory:

# chown postgres:postgres pgsql
chown: changing ownership of 'pgsql': Permission denied

Is it possible to change owner of mounted directory?

回答1:

In IBM Containers, the user namespace is enabled for docker engine. When, the user namespace is enabled, the effective root inside the container is a non-root user out side the container process and NFS is not allowing the mapped non-root user to perform the chown operation on the volume inside the container. Please note that the volume pgdata is a NFS, this can verified by executing mount -t nfs4 from container.

You can try the workaround suggested for How can I fix the permissions using docker on a bluemix volume?

In this scenario it will be

1. Mount the Volume to `/mnt/pgdata` inside the container

cf ic run --volume pgdata:/mnt/pgdata -p 22 registry.ng.bluemix.net/ruimo/pgsql944-cli

2. Inside the container

2.1 Create "postgres" group and user    
groupadd --gid 1010 postgres
useradd --uid 1010 --gid 1010 -m --shell /bin/bash postgres

2.2 Add the user to group "root"
adduser postgres root
chmod 775 /mnt/pgdata

2.3 Create pgsql directory under bind-mount volume
su -c "mkdir -p /mnt/pgdata/pgsql" postgres
ln -sf /mnt/pgdata/pgsql /var/pgsql

2.2 Remove the user from group "root"
deluser postgres root
chmod 755 /mnt/pgdata

回答2:

In your Dockerfile you can modify the permissions of a directory.

RUN chown postgres:postgres pgsql

Additionally when you ssh in you can modify the permissions of the directory by using sudo. sudo chown postgres:postgres pgsql

回答3:

Here are 3 different but possible solutions:

1. Using a dockerfile and doing a chown before mounting the volume.
2. USER ROOT command in dockerfile before you do a chown.
3. Use --cap-add flag.