Current File : //usr/share/doc/debianutils/README.shells
/etc/shells micropolicy
The expected audience of this is debian developers packaging programs
meant to be used as login shells.
/etc/shells is no longer a config file, but is maintained by the
add-shell, remove-shell and update-shells programs. So, if a
package contains something that the maintainer thinks ought to be a
valid login shell, it can have its shell included in two different way.
By placing a fragment in /usr/share/debianutils/shells.d/<binarypackage>,
it will invoke a file trigger on debian-utils and invoke update-shells,
which will add and remove the contained shells from /etc/shells as
needed.
Alternatively, it's postinst should, (on initial install only, to allow a
sysadmin to take it out again), run:
/usr/sbin/add-shell /path/to/shell
In the postrm, probably on remove, the package should call
/usr/sbin/remove-shell /path/to/shell
The latter method has the disadvantage of shells disappearing from /etc/shells
when the relevant package is removed but not purged and then reinstalled. The
fragment method does not suffer from this limitation.
Mini Shell