If you changed root's shell to a non-existent shell in previous Solaris releases, you were forced to boot the system from a local CD or from the network and correct the root shell entry in the /etc/passwd file.
If you mistakenly provide a non-existent shell for root in the Solaris 9 release, root's shell will automatically fall back to /sbin/sh when one of the following occurs:
You use the su command to change to the superuser (root) account.
You are prompted for the root password at the single-user mode password prompt.
For more information, see su(1M).