I've been working on this one for a few days, but no luck. I really need to fix this, as I am now doing everything as root, and it's making me sweat bullets. Here's what I did. I untarred the latest fglrx driver onto my machine after running alien --to-tgz on it. About then, blender took a crap, as it is wont to do, locking up my xsession. Not having any boxen available to ssh in from I had to do a hard reboot (CTL-ALT-F1 doesn't respond when blender hoses my xsession)

When I rebooted, only root could log in. This problem occurs before and after removing all the fglrx stuff that I dropped onto my system and reinstalling libglu1-xorg and libglu1-xorg-dev from debian testing. It also occurs when running both locally compiled kernels and 2.6.14. I did a wajig integrity and didn't find anything awry, also combed /var/log (more on that later). Everything looks just fine. Here's the meat:

tower:/root# sudo -u jbabcock ls
sudo: unable to execute /bin/ls: Permission denied
tower:/root# ls -l /bin/ls
-rwxr-xr-x 1 root root 71996 Sep 3 21:32 /bin/ls
tower:/root# su jbabcock
No shell
tower:/root# grep jbabcock /etc/passwd
jbabcock:x:1000:1000:Josh Babcock,,,:/home/jbabcock:/bin/bash
tower:/root# ls -l /bin/bash
-rwxr-xr-x 1 root root 649556 Oct 13 13:58 /bin/bash
tower:/root# grep bash /etc/shells
tower:/root# login
tower login: jbabcock
Last login: Sun Oct 30 16:54:00 2005 on tty1
Linux tower 2.6.14 #3 PREEMPT Sun Oct 30 18:09:27 EST 2005 i686 GNU/Linux

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
No mail.
Cannot execute /bin/bash: Permission denied
tower:/root# bash
tower:root# exit
tower:/root# sudo -s bash jbabcock
/bin/bash: /bin/bash: cannot execute binary file
tower:/root# ls -ld /
drwxr-xr-x 26 root staff 720 Oct 30 14:21 /
tower:/root# ls -ld /bin
drwxr-xr-x 2 root root 2488 Oct 30 14:42 /bin
tower:/root# tail /var/log/auth.log
Oct 30 18:59:28 tower sudo: root : TTY=pts/0 ; PWD=/root ; USER=jbabcock ; COMMAND=/bin/ls
Oct 30 18:59:40 tower su[3992]: + pts/0 root:jbabcock
Oct 30 18:59:40 tower su[3992]: (pam_unix) session opened for user jbabcock by (uid=0)
Oct 30 18:59:40 tower su[3993]: Cannot execute /bin/bash
Oct 30 18:59:40 tower su[3992]: (pam_unix) session closed for user jbabcock
Oct 30 18:59:54 tower login[3994]: (pam_unix) session opened for user jbabcock by (uid=0)
Oct 30 18:59:54 tower login[3994]: (pam_unix) session closed for user jbabcock
Oct 30 19:00:31 tower sudo: root : TTY=pts/0 ; PWD=/root ; USER=root ; COMMAND=/bin/sh bash jbabcock

That's pretty much everything I could think of testing. Does anyone have *any* idea what the system thinks that no-one but root has permission to execute anything? I am truly vexed. Oh, and to make matters worse, I only have my most important backups, the one with all the binaries and (dammit) the whole debian package status in /var got nixed because I don't currently have enough disk space to hold it and I never got around to implementing a regular DVD burning schedule. At least I have /home and /etc. At least now that I have less to lose I finally sorted out my LVM comfiguration and now have the room I need to make a big ISO so I can burn backup DVDs. There's always a silver lining :)