I haven't dug into this deeply, but we were discussing this in the maintainers meeting (/cc @cpuguy83).

Currently, the "rootless" install script (https://github.com/docker/docker-install/blob/master/rootless-install.sh) is designed such that no root permissions are needed to install everything for running docker in rootless mode.

While this is one scenario, another scenario could be that docker is installed the "regular" way, but now the user wants to either;

1. disable the regular docker service, and instead run rootless, or
2. run additional (rootless) instances

We should investigate if those scenarios are possible:

• should additional things be added to the .deb / .rpm packages (so that users have everything they need if they want to give "rootless" mode a spin)
  • if so, we could bundle them, e.g., in a contrib directory somewhere
• would there be permission issues with files installed by the .deb / .rpm packages that need to be addressed?
• (for 1. above); write instructions how to disable the regular docker (and containerd) services / systemd units
• document how to create a new docker context so that the user can switch between the "host" (rootful) daemon and "rootless" daemon (if both are running)
• other things?

I think that having the option to run docker in rootless mode (after doing a regular install) would be useful to have: it would make it easier to give it a try, and possibly lead to more users testing / trying it.

@AkihiroSuda ptal (you most likely know what would be needed)