Unix security additions

[Chris Siebenmann]

sgf at cfm.brown.edu (Sam Fulcomer) writes:
[In a discussion of secure backups if you don't necessarily trust your
 operators:]
| Why bother having the operator log in? Have the machines reboot at
| backup time, but with the backup program switched on in the rc (or
| inittab, or whatever...).  After backups are done the machine can come
| up normally. Fine if you want to encrypt the dump, too.

 We do something very similar to this, although for different reasons
(and without the encryption) on a set of student systems. We have
Exabytes for backups, and I wanted to do the backups in single-user
mode. However, the student systems don't have operators around them 24
hours a day; the site person works 9 to 5. The solution was to write a
script that backed up everything (with error checking and logs) to
tape, and another script that did some setup, touched a file off in a
mounted filesystem, and started up a shutdown to single-user mode at
some future time. When the system goes single-user, it runs /.profile,
which checks to see if the file exists; if so, it runs the backup
script and then reboots multiuser.

 So the site person pops the right tape into the drive and queues up the
shutdown-backup before he goes home. Sometime later (typically midnight
these days) the system goes down to single-user mode, backs stuff up,
ejects the tape, and goes back to multi-user mode, all without anyone
around. It's quite nice and very convenient.

 But, you ask, what happens if the system crashes and comes up single-
user in the meantime -- won't it start running the backups? That's
why the trigger file is off in a mounted filesystem, instead of on
the root partition; if the system crashes and reboots single-user,
that partition won't be mounted when /.profile is run, so nothing bad
happens.

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