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Most Rootless Containers implementations need the $XDG_RUNTIME_DIR environmental variable to be set. When the environment variable is not set, features related to systemd and cgroups are unlikely to work properly.

The value is typically set to /run/user/$UID automatically by systemd or elogind on logging into the host.

Run the following command to confirm:

$ echo $XDG_RUNTIME_DIR
/run/user/1000

The $XDG_RUNTIME_DIR environmental variable is set when:

• Logged in as a non-root user via the graphic console .
• Logged in as a non-root user via ssh <user>@<hostname> .
• Logged in as the root, and then switched to a non-root user via machinectl shell <user>@ .

The environmental variable is not set when:

• Logged in as the root, and then switched to a non-root user via su -l <user>
• Logged in as the root, and then switched to a non-root user via sudo -u <user>
• Logged in as the root, and then switched to a non-root user via ksu <user>

TL;DR

Don’t use su and sudo for switching from root to non-root.

Use machinectl shell <user>@ or ssh <user>@localhost instead.

To run containers automatically on system start-up, the following command needs to be executed.

$ sudo loginctl enable-linger $(whoami)

Enabling dbus user session is typically needed for using systemd and cgroup v2. Otherwise runc may fail with an error like read unix @->/run/systemd/private: read: connection reset by peer: unknown.

$ systemctl --user is-active dbus
active

$ sudo apt-get install -y dbus-user-session

$ sudo dnf install -y dbus-daemon

In most cases, the dbus user session should be automatically enabled after installing the package above and relogging in. If not, try running systemctl --user start dbus. On some distributions, you may need systemctl --user enable --now dbus too.