keytool error: java.io.FileNotFoundException (Permission denied) while calling from docker file

Resolve 'java.io.FileNotFoundException (Permission denied)' Error with Keytool in Docker

Encountering the 'java.io.FileNotFoundException (Permission denied)' error while calling keytool from a Dockerfile can be frustrating. However, the solution is quite straightforward. Let's dive into the details.

The Root of the Issue

The crux of the problem lies in the default user in Docker, which is 'root'. If your organization has implemented enhanced security measures, it's likely that the user has been changed from 'root' to something else.

When you attempt to execute keytool commands, you face permission denied errors because the current user lacks the necessary privileges. To rectify this, we need to temporarily switch to the 'root' user and then revert back to the original user.

Step-by-Step Resolution

To resolve the error effectively, follow these steps:

1. Establish the Java Environment:
   In your Dockerfile, set the JAVA_HOME environment variable to point to the Java installation directory. For instance:

ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64

2. Copy Certificates:
   Copy the required certificates to the appropriate directory within the container's file system.
3. Switch to 'root' User:
   Use the 'USER root' directive to temporarily change to the 'root' user.
4. Install Certificates:
   Execute keytool commands to install the certificates. Remember to specify the correct arguments, such as the keystore location, password, and certificate file paths.
5. Revert to Original User:
   Once the certificates have been installed, switch back to the original user using the 'USER oldUser' directive.