From owner-freebsd-hackers  Thu Apr 15 20:35:18 1999
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Subject: Entombing for FreeBSD
From: "Andrew J. Korty" <ajk@purdue.edu>
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Date: Thu, 15 Apr 1999 22:32:55 -0500
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Here at the Physics Computer Network, we've been experimenting with
building Kevin Braunsdorf's file entombing system into FreeBSD.
Entombing is an ingenious facility that allows a mortal user to
recover accidentally deleted or clobbered files.

To make entombing work, we replace the C library wrappers for the
system calls open(), rename(), truncate(), and unlink() (and creat()
on systems that have it) with versions that archive the file in a
repository before doing the bona fide syscall.  Each filesystem
with entombing support has its own repository, usually located in
a subdirectory of the filesystem root called "tomb".  This tomb is
owned by a special pseudo-user (charon :-).  The actual moving of
the file is done by a setuid-charon executable so that the files
may be chowned away from the user.  Thus, the file (now called a
"crypt") is no longer counted against the user's quota.  A crypt
is kept in its tomb for a duration inversely related to its size
and the used space on the filesystem.  The "preend" daemon is
responsible for the task of purging old crypts.

The setuid-charon "unrm" command allows users to list, purge, and
restore crypts.  Because files are given unique names when entombed,
arbitrary versions of a file may be restored.  Entombing can be
configured and disabled by the user through the environment variable
ENTOMB.

We think entombing is an elegant solution for a very common problem.
It saves users time because it makes most of their mistakes
reversible.  Systems administrators profit as well, since entombing
allows them to avoid the time-consuming task of restoring files
from tape.  I can't remember the last restore I did!

If this sounds like it would be worth committing, let me know, and
we'll contrib the source patches.  The only changes are the added
code in src/contrib and changes to a few libc Makefiles.  There
are no kernel mods.

Andrew J. Korty, Director     http://www.physics.purdue.edu/~ajk/
Physics Computer Network            85 73 1F 04 63 D9 9D 65
Purdue University                   65 2E 7A A8 81 8C 45 75


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