Switching users inside Docker image to a non-root user

Question

I m trying to switch user to the tomcat7 user in order to setup SSH certificates   When I do su tomcat7  nothing happens   whoami still ruturns root after doing su tomcat7  Doing a more  etc passwd  I get the following result which clearly shows that a tomcat7 user exists   root x 0 0 root  root  bin bash daemon x 1 1 daemon  usr sbin  bin sh bin x 2 2 bin  bin  bin sh sys x 3 3 sys  dev  bin sh sync x 4 65534 sync  bin  bin sync games x 5 60 games  usr games  bin sh man x 6 12 man  var cache man  bin sh lp x 7 7 lp  var spool lpd  bin sh mail x 8 8 mail  var mail  bin sh news x 9 9 news  var spool news  bin sh uucp x 10 10 uucp  var spool uucp  bin sh proxy x 13 13 proxy  bin  bin sh www-data x 33 33 www-data  var www  bin sh backup x 34 34 backup  var backups  bin sh list x 38 38 Mailing List Manager  var list  bin sh irc x 39 39 ircd  var run ircd  bin sh gnats x 41 41 Gnats Bug-Reporting System  admin   var lib gnats  bin sh nobody x 65534 65534 nobody  nonexistent  bin sh libuuid x 100 101   var lib libuuid  bin sh messagebus x 101 104   var run dbus  bin false colord x 102 105 colord colour management daemon     var lib colord  bin false saned x 103 106   home saned  bin false tomcat7 x 104 107   usr share tomcat7  bin false   What I m trying to work around is this error in Hudson    Command  git fetch -t git          co za                       git  refs heads   refs remotes origin    returned status code 128  Host key verification failed    This is my Dockerfile  it takes an existing hudson war file and config that is tarred and builds an image  hudson runs fine  it just can t access git due to certificates not existing for user tomcat7   FROM debian wheezy    install java on image RUN apt-get update RUN apt-get install -y openjdk-7-jdk tomcat7    install hudson on image RUN rm -rf  var lib tomcat7 webapps   ADD   ROOT tar gz  var lib tomcat7 webapps     copy hudson config over to image RUN mkdir  usr share tomcat7  hudson ADD   dothudson tar gz  usr share tomcat7  RUN chown -R tomcat7 tomcat7  usr share tomcat7     add ssh certificates RUN mkdir  root  ssh ADD ssh tar gz  root     install some dependencies RUN apt-get update RUN apt-get install --y maven RUN apt-get install --y git RUN apt-get install --y subversion    background script ADD run sh  root run sh RUN chmod  x  root run sh    expose port 8080 EXPOSE 8080   CMD    root run sh     I m using the latest version of Docker  Docker version 1 0 0  build 63fe64c 1 0 0   is this a bug in Docker or am I missing something in my Dockerfile

User · Answer

As a different approach to the other answer, instead of indicating the user upon image creation on the Dockerfile, you can do so via command-line on a particular container as a per-command basis.

With docker exec, use --user to specify which user account the interactive terminal will use (the container should be running and the user has to exist in the containerized system):

docker exec -it --user [username] [container] bash

See https://docs.docker.com/engine/reference/commandline/exec/

User · Answer

In case you need to perform privileged tasks like changing permissions of folders you can perform those tasks as a root user and then create a non-privileged user and switch to it  From  lt some-base-image tag gt     Switch to root user USER root    lt --- Usually you won t be needed it - Depends on base image    Run privileged command RUN apt install  lt packages gt  RUN apt  lt privileged command gt     Set user and group ARG user appuser ARG group appuser ARG uid 1000 ARG gid 1000 RUN groupadd -g   gid    group  RUN useradd -u   uid  -g   group  -s  bin sh -m   user     lt --- the  -m  create a user home directory    Switch to user USER   uid    gid     Run non-privileged command RUN apt  lt non-privileged command gt

User · Answer

There s no real way to do this   As a result  things like mysqld safe fail  and you can t install mysql-server in a Debian docker container without jumping through 40 hoops because   well    it aborts if it s not root   You can use USER  but you won t be able to apt-get install if you re not root

User · Answer

You should also be able to do   apt install sudo  sudo -i -u tomcat  Then you should be the tomcat user   It s not clear which Linux distribution you re using  but this works with Ubuntu 18 04 LTS  for example

User · Answer

Add this line to docker file   USER  lt your user name gt    Use docker instruction USER

User · Answer

You should not use su in a dockerfile  however you should use the USER instruction in the Dockerfile   At each stage of the Dockerfile build  a new container is created so any change you make to the user will not persist on the next build stage   For example   RUN whoami RUN su test RUN whoami   This would never say the user would be test as a new container is spawned on the 2nd whoami  The output would be root on both  unless of course you run USER beforehand    If however you do   RUN whoami USER test RUN whoami   You should see root then test   Alternatively you can run a command as a different user with sudo with something like  sudo -u test whoami   But it seems better to use the official supported instruction

[git] Switching users inside Docker image to a non-root user

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