shells - shell database
The shells file contains a list of the shells on the system. Applications use this file to determine whether a shell is valid. For each shell a single line should be present, consisting of the shell's path, relative to root. For more information, see the getusershell(3C) man page.
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.
The following default shells are used by utilities: /bin/bash, /bin/csh, /bin/jsh, /bin/ksh, /bin/ksh93, /bin/pfcsh, /bin/pfksh, /bin/pfsh , /bin/sh, /bin/tcsh, /bin/zsh, /sbin/jsh, /sbin/sh, /usr/bin/bash, /usr/bin/csh, /usr/bin/jsh, /usr/bin/ksh, /usr/bin/ksh93, /usr/bin/pfcsh, /usr/bin/pfksh, /usr/bin/pfsh, and /usr/bin/sh, /usr/bin/tcsh, and /usr/bin/zsh. The /etc/shells overrides the default list.
Invalid shells in /etc/shells could cause unexpected behavior, such as being unable to log in by way of ftp(1).
list of shells on system