After the user logs in, a process must be started, which is responsible for transmitting the user's operations to the kernel. This process is a command interpreter or a specific program, that is, Shell, that is run after the user logs in to the system. Shell is the interface between users and Linux systems. There are many types of Linux Shells, each with different characteristics. Commonly used ones include sh(BourneShell), csh(CShell), ksh(KornShell), tcsh(TENEX/TOPS-20typeCShell), bash(BourneAgainShell), etc. System administrators can designate a shell for users based on system conditions and user habits. If you do not specify a shell, the system uses sh as the default login shell, that is, the value of this field is /bin/sh.
This is the program to run at login (if empty, use /bin/sh). If set to a nonexistent executable, the user will be unable to login through login(1). The value in this field is used to set the SHELL environment variable.
No
/bin/bash
will specify the defaulthttp://moper.me/detailed-description-etc-passwd-file.html
Reference http://linux.die.net/man/5/passwd