The /sbin/nologin for Fedora and /usr/sbin/nologin for Debian are two shells that return you a polite message like “this account is not available” and do not allow you to log into the system. This message can be customized.
/bin/false is an old shell used to deny a user’s login. The /bin/false exits immediatly when false exists. The user accounts with /bin/false or /bin/true as their default shells are locked.
/sbin/nologin belongs to unix-linux while /bin/false part of GNU Coreutils. These shells must be listed in the /etc/shells file, to work.
The users with /sbin/nologin (or /usr/sbin/nologin) can connect through ssh or ftp, but the users with /bin/false are completely locked out from the system.
Users can also be locked with the passwd -l command:
How to lock a user:
$ sudo passwd -l UserName
How to unlock a user:
$ sudo passwd -u UserName