SFILL(1)SFILL(1)NAMEsfill - secure free disk and inode space wiper (secure_deletion tool‐
kit)
SYNOPSISsfill [-f] [-i] [-I] [-l] [-l] [-v] [-z] directory/mountpoint
DESCRIPTIONsfill is designed to delete data which lies on available diskspace on
mediums in a secure manner which can not be recovered by thiefs, law
enforcement or other threats. The wipe algorythm is based on the paper
"Secure Deletion of Data from Magnetic and Solid-State Memory" pre‐
sented at the 6th Usenix Security Symposium by Peter Gutmann, one of
the leading civilian cryptographers.
The secure data deletion process of sfill goes like this:
* 1 pass with 0xff
* 5 random passes. /dev/urandom is used for a secure RNG if avail‐
able.
* 27 passes with special values defined by Peter Gutmann.
* 5 random passes. /dev/urandom is used for a secure RNG if avail‐
able.
afterwards as many temporary files as possible are generated to wipe
the free inode space. After no more temporary files can be created,
they are removed and sfill is finnished.
COMMANDLINE OPTIONS-f fast (and insecure mode): no /dev/urandom, no synchronize mode.
-i wipe only free inode space, not free disk space
-I wipe only free disk space, not free inode space
-l lessens the security. Only two passes are written: one mode with
0xff and a final mode with random values.
-l-l for a second time lessons the security even more: only one
random pass is written.
-v verbose mode
-z wipes the last write with zeros instead of random data
directory/mountpoint this is the location of the file created in your
filesystem. It should lie on the partition you want to write.
LIMITATIONS
FILESYSTEM INTELLIGENCE
Most filesystems (ext2, ffs, etc.) have several features
included to enhance performance, which will result in that sfill
might not receive all available free space. Sad but true. Noth‐
ing can be done about that ...
NFS Beware of NFS. You can't ensure you really completely wiped your
data from the remote disks. (especially because of caching)
Raid Raid Systems use stripped disks and have got large caches. It's
hard to wipe them.
swap Some of your data might have a copy in your swapspace. sswap is
available for this task.
BUGS
No bugs. There was never a bug in the secure_deletion package (in con‐
trast to my other tools, whew, good luck ;-) Send me any that you find.
Patches are nice too :)
AUTHOR
van Hauser / THC <vh@thc.org>
DISTRIBUTION
The newest version of the secure_deletion package can be obtained from
http://www.thc.org
sfill and the secure_deletion package is (C) 1997-2003 by van Hauser /
THC (vh@thc.org)
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; Version 2.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MER‐
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.
SEE ALSO
srm (1), sswap (1), smem (1)
SFILL(1)
