Podman warns cgroupv2 manager is set to systemd without a user session

This document (000021071) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP3

Situation

When a non-root user runs podman, the following warnings are observed.

> podman images
WARN[0000] The cgroupv2 manager is set to systemd but there is no systemd user session available
WARN[0000] For using systemd, you may need to login using an user session
WARN[0000] Alternatively, you can enable lingering with: `loginctl enable-linger 1000` (possibly as root)
WARN[0000] Falling back to --cgroup-manager=cgroupfs
WARN[0000] The cgroupv2 manager is set to systemd but there is no systemd user session available
WARN[0000] For using systemd, you may need to login using an user session
WARN[0000] Alternatively, you can enable lingering with: `loginctl enable-linger 1000` (possibly as root)
WARN[0000] Falling back to --cgroup-manager=cgroupfs
REPOSITORY TAG IMAGE ID CREATED SIZE

No warnings are given for running the command as root.

The kernel command line shows that cgroups v2 have been enabled using systemd.unified_cgroup_hierarchy=1.

# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-5.14.21-150400.24.63-default root=UUID=1724a83c-cacd-4d56-8f70-119492248191 nosplash mitigations=auto systemd.unified_cgroup_hierarchy=1

The error is observed on SLES 15 SP3 and SP4, but not on SLES 15 SP1 and SP2.

Resolution

Logout of all users and login directly as the desired user. Repeat the command.

Cause

The root user ran su - <user> and tried to run podman. As a result, the systemd user session was not available.

Disclaimer

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