Question

From inside a container, I would like to get the id of a user on the host machine (what the command id -u username would output, from the host).

Is there a way to accomplish this?

I thought I could mount /etc/passwd in the container and grep inside, but unfortunately the users are not listed in this file on our server (possibly related to the LDAP authentication mechanism?).

Thanks

asked Apr 9, 2020 at 16:08

brunobruno

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Answer 1

I ended up solving this by mounting host folder /home on my container, and getting the id of the owner of user's home dir /home/<user>.

answered Apr 17, 2020 at 8:22

brunobruno

695 bronze badges

Answer 2

There's no way to get information about host users from inside a container. A design goal of Docker is that the host and containers are isolated from each other. A container has no concept of a host user; from the Docker daemon point of view, Docker doesn't even really know which user requested that a container be launched.

(This is doubly true if your host authentication system is something more complicated like an LDAP setup: a container simply may not have the tools or credentials required to query it, and the isolation means there's no way to somehow delegate to the host.)

If a principal goal of your application is to interact with host users, or the host filesystem, or you otherwise actively don't want Docker's isolation features, it's better to run your program outside of Docker.

answered Apr 9, 2020 at 17:46

David MazeDavid Maze

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