[SOLVED] Cannot create directory. Permission denied inside docker container

Cannot create directory. Permission denied inside docker container

Can not create folder during image building with non root user added to sudoers group. Here is my Dockerfile:

FROM ubuntu:16.04

RUN apt-get update && \
    apt-get -y install sudo

RUN adduser --disabled-password --gecos '' newuser \
    && adduser newuser sudo \
    && echo '%sudo ALL=(ALL:ALL) ALL' >> /etc/sudoers

USER newuser

RUN mkdir -p /newfolder
WORKDIR /newfolder

I get error: mkdir: cannot create directory '/newfolder': Permission denied

Solution

Filesystems inside a Docker container work just like filesytems outside a Docker container: you need appropriate permissions if you are going to create files or directories. In this case, you're trying to create /newfolder as a non-root user (because the USER directive changes the UID used to run any commands that follow it). That won't work because / is owned by root and has mode dr-xr-xr-x.

Try instead:

RUN mkdir -p /newfolder
RUN chown newuser /newfolder
USER newuser
WORKDIR /newfolder

This will create the directory as root, and then chown it.