SSH System Bootup In Progress Please Wait Error and Solution

Q. I've Debian Linux server and whenever someone trying to ssh into this box, they get an error as follows and server closes the connection:

System bootup in progress -please wait

How do I fix this problem and allow ssh login?

A. This error appers when system config or root user creates /etc/nologin file. If the file /etc/nologin exists, login will allow access only to root. Other users will be shown the contents of this file and their logins will be refused. The solution is simple, delete the file /etc/nologin manually:
rm /etc/nologin
If this error occurs after reboot open /etc/default/rcS file and set DELAYLOGIN to no:
DELAYLOGIN=no
If this option set to yes, /etc/init.d/bootmisc.sh will create /etc/nologin, which causes a default SSH and PAM configuration to prevent all logins.
This problem cannot be solved over remote ssh session. However, if you can login via KVM or serial console, then you can fix it over remote session.