in terminal I get everything running normally and then:
All processes ended withing 2 seconds...done INIT: Going single user INIT: Sending processes the TERM signal INIT: Sending processes the KILL signal Give root password for maintenance(or....
I press Ctrl + D, and it shows me login screen Debian. Shutdown through GUI works properly.
It seems some process hangs.
Moreover, I've managed to power off the server through several retries. Recently I've installed only ntp and ntpdate, nothing more.
I suppose it might be it conflicting with iptables.