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 through login(1). The value in this field is used to set the through SHELL environment variable.
沒有
/bin/bash
會指定預設的http://moper.me/detailed-description-etc-passwd-file.html
參考http://linux.die.net/man/5/passwd