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.
- A student trying to restore from a removal of his / partition
installed the OS from the distribution. He then attempted to
restore / from a bacula backup. As he discovered, trying to
copy over all the files in / while the system is running is
not to good. Some of the files (like the kernel and the
modules) really shouldn't be copied over while the kernel
is executing.
- Another student, having learned from the above student's problem
did something similar, but instead of copying over /, decided to
restore to another directory. Strangely enough, however, the
directory that was created by the restore was in /, but it was
named "/". (I didn't even know that was possible.) He then
attempted to remove it by executing "rm -r //" with predictable
results. He was down to only having /home left when he figured
out what was going on.
- 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).
- 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.
- 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.