How can I remove this annoying message: "Failed to find cgroup2 mount"?

I run this command ss -tulpnoea|grep -i water|grep -v 127 Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount ..... I tried with 2> /dev/null... ss -tulpnoea|grep -i water|grep -v 127 2> /dev/null Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount Failed to find cgroup2 mount ..... How to avoid the annoying message about cgroup2 mount? Distro is Slackware 15.0