Check an update of an RPM without actually updating it

yum check-update  

Delete an RPM that was already deleted from the file system

rpm -e --justdb

Restart OpenStack Cinder Services in Red Hat Linux / CentOS

systemctl stop openstack-cinder-api.service

systemctl stop openstack-cinder-scheduler.service

systemctl stop openstack-cinder-volume.service

systemctl stop openstack-cinder-backup.service

systemctl start openstack-cinder-api.service

systemctl start openstack-cinder-scheduler.service

systemctl start openstack-cinder-volume.service

systemctl start openstack-cinder-backup.service

systemctl enable openstack-cinder-api.service

systemctl enable openstack-cinder-scheduler.service

systemctl enable openstack-cinder-volume.service

systemctl enable openstack-cinder-backup.service

How to boot CentOS v7.x to single user mode

• Press e
• In the line that starts with linux16, modify ro to rw init=/sysroot/bin/sh
• CTRL-X
• chroot /sysroot/
• reboot -f

For more information:

https://www.tecmint.com/boot-into-single-user-mode-in-centos-7/