Suppress the output of the RUN command in a Dockerfile

Question

How can I suppress the output of the RUN command in a Dockerfile? In the code below, I'm attempting to redirect the SSH_PRIVATE_KEY to a file using the echo command. However, during image building, the Docker logs reveal the SSH PRIVATE KEY, which I'd like to avoid. Is there a way to silence the RUN command in a Dockerfile, or is there another solution to this issue?

RUN echo "${SSH_PRIVATE_KEY}" > /home/$USER/.ssh/id_ed25519

Build log

 => CACHED [app 10/19] RUN echo "-----BEGIN OPENSSH PRIVATE KEY-----0s9               0.0s

Since anyone who gets a copy of the image can trivially extract files from it, your ssh key is already compromised if you do this. Make sure to properly revoke the key anywhere you might have used it. Do not pass credentials like this as Dockerfile ARG or otherwise supply them to the build process. — David Maze
– David Maze, Commented Jan 18, 2024 at 20:32
Try this RUN bash -c 'echo "${SSH_PRIVATE_KEY}" > /home/$USER/.ssh/id_ed25519' to see if it works. — Philippe
– Philippe, Commented Jan 18, 2024 at 21:43

tripleee · Accepted Answer · 2024-01-18 13:49:17Z

2

A simple workaround is to have the key in a file instead in the first place.

COPY privkey /home/$USER/.ssh/id_ed_25519

with privkey obviously in a local file in the directory where you run docker build et al.

answered Jan 18, 2024 at 13:49

tripleee

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