Sometimes invoking 'su' fails. This can be caused by a number of things. Before you look for the cause you might...
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.
want to try: "su -m" (Leave the environment unmodified.) This Berkeley 'su' option appears to be an undocumented one of SunOS too.
$ su -
$ su -m