XDG_RUNTIME_DIR isn't set for root user, logged in via sudo inside SSH session

[danbst]

My setup (pretty scary):

• Ubuntu 18.04
• connect to remote host as ubuntu user
• sudo su - to obtain root
• home-manager with some 18.09 checkout installed into root-s home
• custom user service defined
• linger enabled:

    home.activation.linger = dag.entryBefore ["reloadSystemD"] ''
        loginctl enable-linger $USER
    '';

I get a problem that systemctl --user can't reach DBus:

root@nomad-02:~# systemctl --user -a
Failed to connect to bus: No such file or directory

I fix it with

    home.sessionVariables.XDG_RUNTIME_DIR = "/run/user/$UID";

but I wonder why this isn't default.

[wedens]

You don't even need to do that remotely.

Doing something like sudo -u other_user zsh -c 'systemctl --user show-environment' will result in the same problem. Providing XDG_RUNTIME_DIR makes it work.

[rycee]

Seems this is (mostly) by design. See, e.g., systemd/systemd#7451 (comment)

Specifically, the su and sudo PAM configurations intentionally don't include pam_systemd.so (at least on NixOS) so XDG_RUNTIME_DIR will not be set for those commands. You can bypass this by setting XDG_RUNTIME_DIR as you've found out but reading Poettering's response it seems to me that this comes with implications that makes it a bad idea to include it by default in HM.

Using machinectl does indeed seem to work to give you a proper login shell with a functional systemd. E.g.

$ machinectl shell test@

to make a login shell for the user "test" on the local system. So I would suggest using machinectl instead of sudo when you want a full login shell with a user systemd session. This seems like an extra good idea for root logins since the machinectl way appears to isolate the root login more from your user login.

[danbst]

interesting. So sudo su - considered wrong, use sudo machinectl shell root@...

[wedens]

One of the problems with machinectl shell is that it doesn't propagate exit code, if you care about it. man says that systemd-run should be used in this case, but I can't figure out the correct way to use it.

[stale]

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