Add more detailed explanations on the reasons why sudo should be avoided

[VonUniGE]

If sudo is included in a command, dockerfilelint outputs the following message:

Avoid installing or using sudo since it has unpredictable TTY and signal-forwarding behavior that can cause problems. If you absolutely need functionality similar to sudo, such as initializing the daemon as root but running it as non-root), consider using “gosu”.

This message should give more detailed explanations (or a link) on the reasons why sudo should be avoided.

There is also a question about this on unix.stackexchange.com : What exactly in the sudo behavior is unpredictable?

[SISheogorath]

This is actually a quote from the official docker best practices:

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#user

To see the official reasoning in all detail I recommend to have a look at the gosu repository:
https://github.com/tianon/gosu#gosu

[VonUniGE]

Ok, the source of the message is the official Docker documentation. But, I cannot find in the gosu repository the reasoning you mention. Can you make a citation with this reasoning?

[SISheogorath]

Have a look at the "Why?" Section of the gosu readme. It refers to a dockerfile for testing purposes. These are all kinds of edge cases that cause problems with `sudo`. For a detailed description of what complicated behavior `sudo` implies I recommend to read the sudo man-page and their detailed description about signal handling and process model.

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On 12 April 2018 09:26:05 GMT+02:00, VonUniGE ***@***.***> wrote: Ok, the source of the message is the official Docker documentation. But, I cannot find in the gosu repository the reasoning you mention. Can you make a citation with this reasoning?

-- Signed Sheogorath Sent from my Android device with K-9 Mail. Please excuse my brevity.

[VonUniGE]

Thank you for your answer.

I understand that sudo is too heavy and complicated if the only goal is to drop privileges from root to a user. But if we want to test an application in different dockerized linux distributions, I think that sudo can still be useful.

I would like that dockerfilelint gives a more detailed explanation here, in order to let the user make an informed choice and not just follow a recommendation for which he doesn't understand the reasons.

But for now, I have no better formulation to propose...