Dropping privileges for $USER

[DarkGhostHunter]

Basically, I'm trying to make a development container that runs both PHP Built-In Server and an SSH Server.

The problem is that v3 doesn't like the USER directive in the Dockerfile. While services can run as $USER, I'm trying to make all commands sent as docker run are run as $USER.

I don't know if when calling commands the services set in s6-overlay/s6-rc.d run or not. Also, I don't know if there is a way to proxy a command as non-root while running some required scripts before running the command, like creating the $USER in the system and fixing permissions if the developer has set $UID and $GID inside the container.

Is this supported at all, or the only way is to not use S6 at all?

Related to #286

[skarnet]

s6-overlay is definitely supposed to support USER directives in the Dockerfile. Can you post a transcript of the messages you get when you try running a container with USER, preferably with S6_VERBOSITY set to 2 or more?