Systemd-logind

• loginctl

Jan 25 15:58:36 SERVER systemd-logind[876]: Failed to save user data /run/systemd/users/0: No space left on device

See also

• Systemd: systemctl, systemd-journald, journalctl systemd-cat, systemd-logind, systemd-networkd:networkctl, systemd-timesyncd, systemd-resolved, systemd-udevd , Systemd-logind: loginctl, hostnamectl, udevadm, systemd-run, portablectl, systemd-nspawn, systemd resource management, Timer (systemd), systemd logs, /etc/systemd/, systemd services, systemd-mount, /run/systemd/, .service, /usr/lib/systemd/, /usr/lib/systemd/system/, /usr/lib/systemd/system/systemd-resolved.service, /lib/systemd/, machinectl, systemd-oomd, systemd-analyze

https://wiki.ubuntu.com/DebuggingSystemd