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`