这个是apcupsd自动关机后引起的，删除/etc/nologin文件即可。

参考：http://grokbase.com/t/centos/centos/13794mw7jx/centos-6-4-login-after-reboot-after-apcupsd-shutdown-shows-power-failure

Hi list,
just putting a new server through its automatic shutdown triggered by
the UPS / apcupsd.
All worked faultlessly, including powering up when power came back on to
the UPS.


So then I go to log in and get "POWER FAILURE" followed by
"Authentication failure" - this is on the console


via SSH I just get "POWER FAILURE" and the ssh connection drops.


So I guess the, log everyone out and stop further logins instruction is
still lurking around somewhere.


How do I regain control of my server??
Does this mean I need to boot with a rescue disk and edit some file
somewhere??


How do I prevent this re-occurring, after a perfect shutdown and
restart, only to get stymied here.


Google has lots of help for dealing with various corruptions due to
power failure - not the case here, the POST, grub, init restart
all look just fine.
TIA

Sounds like /etc/nologin; contents of which are displayed immediately
before the login session terminates. Configured within apcupsd.conf
with a configuration setting of NOLOGINDIR pointing to /etc by default;
I don't believe it can be disabled, however.