RFE: touch a file to make it easy to tell we're containerized

[jlebon]

/kind feature

Description

AFAICT, there isn't a file like /.dockerenv to make it easy to tell we're in a container. Can we add something like /run/podman-container?

[mheon]

This seems like an easy enough thing to do

[TomSweeneyRedHat]

but /.containerenv or some such?

[jlebon]

That sounds OK too. I find /run nicer to indicate the ephemeral nature of it though that's mostly personal preference. :)

[TomSweeneyRedHat]

/run/.containerenv would be fine by me too. My main thing was to not include the d-word....

[mheon]

Is there anything we should look into including in the file that would be helpful, besides its existence? Podman version, potentially?

[jlebon]

Hmm, how about we just leave it empty for now? Adding things later on if we really want would be a mostly backwards compatible change.

[rhatdan]

Will this work with readonly containers? Should the file be read-only, should we make sure the file does not end up in an image? Putting the file in /run, would be my preferred mechanism to. Adding the version of the tool that created the file inside buildah-1.13 or podman-0.3.3

[nalind]

If we add a file, like dockerd does, but give it a different name, then we're not reducing the amount of work required for anyone. systemd suggests setting container in the environment to a short value that identifies the implementation. Would that work for the use case?

[mheon]

@baude suggested an environment variable would be good to set in addition to the file. It would be easy enough to add both.

[rhatdan]

Yes systemd like container=podman or container=buildah to be set.

[mheon]

Fixed in #533