Panic ! Thats what occurs when a critical systems you manage cannot login , but the service was running properly.Recently i do some changes on the /etc/security/limits.conf and it make all lockout. No SSH can be done, but all the service was running properly.To the rescue, we need to login to the systems and revert back changes, and to do that we need to go into single mode.We do on Centos 7.x systems which is the grub boot loader is different than the old version.So how to do it step by step, and no panic. Reboot your machine and immidiately go to rescue mode.Chose one boot options and press "e" to change the entryLook for below entry :linux16...