Startup script for docker containers to resolve volume permission issues

volume_guid.sh

#!/bin/bash

# Original source of this script: http://stackoverflow.com/questions/23544282/what-is-the-best-way-to-manage-permissions-for-docker-shared-volumes/28596874#28596874
# This will only work for files and folders that allow the group to do what they are trying to do. Wont work on files with 700 permissions for instance.

# Path of mounted volume inside the container
VOLUME_PATH = change/me/path

# Name of user that needs permissions to the volume
USERNAME = changme

# Get the guid of the directory used for the shared volume
TARGET_GID=$(stat -c "%g" /volume/FOOBAR)

# Check if a group exists with the same guid within the container
EXISTS=$(cat /etc/group | grep $TARGET_GID | wc -l)

# Create new group using target GID and add nobody user
if [ $EXISTS == "0" ]; then
  groupadd -g $TARGET_GID tempgroup
  usermod -a -G tempgroup nobody
else
  # GID exists, find group name and add
  GROUP=$(getent group $TARGET_GID | cut -d: -f1)
  usermod -a -G $GROUP $USERNAME
fi