By default when you add new user to system (/etc/passwd file) it grant shell access. If you are creating new users for POP3 or SMTP (mail server) or FTP then you do not need to grant shell access to a user. Remember as soon as you add a user he/she can login via telnet or [...]
You need to use autofs. It is use to mount file system on demand. Usually autofs is invoked at system boot time with the start parameter and at shutdown time with the stop parameter. The autofs script can also manually be invoked by the system administrator to shut down, restart or reload the automounters. autofs [...]