file contains a list of valid shells available on the system.
A shell is a command line interpreter that reads user input and executes
For each shell a single line should be present, consisting of the
shell's path, relative to root.
A hash mark
indicates the beginning of a comment; subsequent
characters up to the end of the line are not interpreted by the
routines which search the file.
Blank lines are also ignored.
program will not let regular users change their default shell to one not
listed in the
daemon denies access to users who are not using one of the listed shells.