allows access to the system by the user root only

PAM NOLOGIN:-

* allows access to the system by the user root only
* obviates the need to shut down services

* displays the contents of /etc/nologin file

sample content of this file :-

CURRENTLY WE ARE UNDERGOING SYSTEM MAINTENANCE, EXPECT US BACK IN 1600 HOURS

add the following directive

auth required pam_nologin.so to the relevant pam file.
(ex:- for ssh /etc/pam.d/sshd file)


[root@BACKUP-SERVER ~]# find / -name pam_nologin.so
/lib64/security/pam_nologin.so
/lib/security/pam_nologin.so