Almost everything is segfaulting after yum update

[David Hagood]

I did a yum update earlier today, and somehow have totally wedged my
computer - many critical programs segfault on startu.

If I start with SELinux enabled, the system does not get its hostname set
(i.e. NIS is broken), and nobody, not even root, can log in. Only if I
disable SELinux at boot can I even log in (yes, I have allowed it to do a
security relabel).

If I disable SELinux at boot, the machine gets its hostname and I can log
in, BUT:

su segfaults for all users other than root.
sendmail immediately segfaults. By "immediately", I mean so immediately
that even "ldd /usr/sbin/sendmail" segfaults.

Logrotate segfaults if I actually ask it to do anything, though it will
run enough to show usage.

Python segfaults - so no YUM.

gdb segfaults - so I cannot get a backtrace on the offending programs.

I'm left to enter this either on my old SGI Indy or my Nokia 770 - which
by an accident of history are roughly the same in CPU power...