How do I recover from filesystem full?

[Robert Prohaska]

While running postinstall for the 2.0.1 upgrade my mac ran out
of disk space in its default 80 meg root partition.  The error
was mine for not removing inc.cpio.Z before running postinstall.

Now, the question is, which way is out?  I removed inc.cpio.Z and
tried to log in as root, but there is no mouse on login, which
makes it hard to start commandshell and redo the upgrade.

can I run postinstall from sash?

bob