On my RHEL7 VM, the reboot took about 30-40 mins to boot up
(was told by colleague who supports it, it's about 20 times longer).
At the console, I could see
"dracut Warning: Cannot umount /oldroot
dracut Warning: Blocking umount of /oldroot 
dracut Warning: lrwxrwxrwx. 1 root 0 0 ...
A few links suggest to disable firewalld but after it boots up, can't
see that firewalld is running:
$ firewall-cmd --list-all |more
FirewallD is not running
is the dracut message on the console the cause of the slow booting
up or this long booting up is caused by another issue? How can I