I'm trying to add a file to a Docker image built from the official
tomcat image. That image does not seem to have root rights, as I'm logged in as user
tomcat if I run bash:
docker run -it tomcat /bin/bash tomcat@06359f7cc4db:/usr/local/tomcat$
If I instruct a
Dockerfile to copy a file to that container, the file has permissions
644 and the owner is
root. As far as I understand, that seems to be reasonable as all commands in the Dockerfile are run as root. However, if I try to change ownership of that file to
tomcat:tomcat, I get a
Operation not permitted error.
Why can't I change the permissions of a file copied to that image?
How it can be reproduced:
mkdir docker-addfilepermission cd docker-addfilepermission touch test.txt echo 'FROM tomcat COPY test.txt /usr/local/tomcat/webapps/ RUN chown tomcat:tomcat /usr/local/tomcat/webapps/test.txt' > Dockerfile docker build .
The output of
docker build .:
Sending build context to Docker daemon 3.072 kB Sending build context to Docker daemon Step 0 : FROM tomcat ---> 44859847ef64 Step 1 : COPY test.txt /usr/local/tomcat/webapps/ ---> Using cache ---> a2ccb92480a4 Step 2 : RUN chown tomcat:tomcat /usr/local/tomcat/webapps/test.txt ---> Running in 208e7ff0ec8f chown: changing ownership of '/usr/local/tomcat/webapps/test.txt': Operation not permitted 2014/11/01 00:30:33 The command [/bin/sh -c chown tomcat:tomcat /usr/local/tomcat/webapps/test.txt] returned a non-zero code: 1