update-shells - update the list of valid login shells

update-shells  locates  the  shells provided by packages from /usr/share/debianutils/shells.d and updates
       /etc/shells with newly added or removed shells.  To track changes made by the administrator, it  consults
       a state file in /var/lib/shells.state.

/etc/shells/var/lib/shells.state/usr/share/debianutils/shells.d

       update-shells - update the list of valid login shells

--no-act
              Do not actually perform the changes to /etc/shells.--rootROOT

              Operate on a chroot at ROOT.  Defaults to the value of the environment variable DPKG_ROOT.--verbose
              Print the shells that are being added or removed.

shells(5)

                                                   28 Jun 2021                                  UPDATE-SHELLS(8)

update-shells [options]