Things Not to Do

I caution my System Administration students not to do anything that will embarrass them later. I go on to say that they won't know which things will cause embarrassment until they do them. I'm reminded of a quote from Run with the Horsemen by Ferol Sams in which Porter Osborne's father says of him, ``Porter's a good boy. He minds well enough. I just can't think of enough things to tell him not to do.''

In any event, what follows is a brief collection of embarrassing moment for some of my students organized by semester of occurrence.

Fall 2000

• A student inadvertently removed /usr/local. This would not normally have been a disaster, but unfortunately, the student had set root's login shell to be /usr/local/bin/bash, thus root could no longer log in.

  Since ftp was enabled on the machine, this was easily resolved by ftping to the machine as root (yes, AIX 4.3.3 allows you to do this), and copying bash to the correct location.

• In gzipping some files, a student accidentally specified the root directory as the source for a recursive gzip and let the process run to completion. Of course, this left the entire filesystem gzipped and no actions could be taken.

  To resolve this situation, the student removed the disk from the machine, mounted the filesystems on another functioning machine, gunzipped all files, then transferred the disk to the original machine and remounted the filesystems.

• Exploiting the absolutely inane ability of mount to mount a filesystem on top of an already mounted filesystem's root (and stack the mounts), a student accidentally mounted a filesystem on top of /.

  Although the student still had a running shell, there was nothing of interest the student could do with a filesystem whose root contained only lost+found. The student was instructed to conduct a manly reboot (power cycling the machine).

Spring 2001

• In attempting to set up their machine's NIS service, one team of students modified their rc.nfs to execute ypbind without modifying it to set the domainname correctly. Of course, this resulted in their machine hanging upon attempting to bind to the server.

  The moral of this story, of course, is that one must be especially careful to make sure the preconditions required or a service are in place before the service is started.

Fall 2001

• Several a group of students collectively believed that, somehow, their root password had been changed or somehow corrupted. Unfortunately, this was on a Sun Netra with no CD, floppy, or other external device besides network. They were then presented with the solution method, namely, getting *another* machine to
  • Provide DHCP service.
  • Make a root partition available for tftp.
  Suddenly, with this extra incentive, the students remembered what they had changed their root password to.