chsh changes the user login shell. This determines the name of the user's initial login command. An unprivileged user may only change the login shell for their own account, a user with appropriate privilege may change the login shell for any account specified by user.
Unless the user has appropriate privilege, the initial login command name shall be one of those listed in /etc/shells. The login_shell shall be the absolute path (i.e. it must start with '/') to an executable file. Accounts which are restricted (in an implementation-defined manner) may not change their login shell.
If the -s option is not selected, chsh operates in an interactive mode. The prompts and expected input in this mode are unspecified.