You start a container with --read-only and try to create a file in /tmp, but get a permission error. What is the most probable reason?

medium📝 Troubleshoot Q6 of 15

Docker - Security

You start a container with --read-only and try to create a file in /tmp, but get a permission error. What is the most probable reason?

A<code>/tmp</code> directory does not exist inside the container.

B<code>/tmp</code> is part of the read-only root filesystem and not mounted as writable.

CThe container is missing network access.

DThe Docker daemon is running in debug mode.

Step-by-Step Solution

Solution:

Step 1: Understand --read-only
The entire root filesystem is read-only, including /tmp, unless explicitly mounted writable.
Step 2: Cause of permission error
Trying to write to /tmp fails because it is not writable.
Final Answer:
/tmp is part of the read-only root filesystem and not mounted as writable. -> Option B
Quick Check:
Writable mounts needed for write access [OK]

Quick Trick: Writable mounts required for /tmp with --read-only [OK]

Common Mistakes:

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