I found a rather easy way to crash a Mac.
First, You need to have two or more partitions.
Second, delete the directory /var/vm.
Third, create a symbolic link. ln -s /The/Other/partition/directory
/var/vm. /The/Other/partition/directory is at another partition other
than the one where /var is at.
Then you continue to use your Mac for some time, you will find at least
one program crashes. Then you may decide to reboot your mac to see
whether the program will become normal, you must find that your mac
could not start again.
Don't be panic. You can solve it. Use your Mac installation disc. But
you don't need to reinstall your system. You can open a terminal, delete
the symbolic link /var/vm and create a new directory /var/vm. Then you
will find your crazy mac become normal.
I think this should be a bug in Mac.
/var/vm is the directory where the swap files are at. Mac seems to use
this directory before it mounts the other partition. So if /var/vm is a
symbolic link to other partition, Mac could not use /var/vm at all when
it starts, because other partitions are not available yet.
And the swap files can become very large. They may use up the all the
disk space. They will make the system rather slow.