The problem that I had, several times, was a shutdown hangup on something like "deconfiguring inetd". At this point, the keyboard was disabled. I could escape to another TTY# but could type nothing. The best behaved shutdown at this point as a control./alt/del. It apparently did not flush the disks.
Alt+SysRq-S-U-B might work better[S syncs the discs, U umounts them, B reboots]. Of course it would probably be best to figure out why deconfiguring inetd is hanging.
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