Discussion on:

Securely delete files with shred

Shred, from their own man page,

CAUTION: Note that shred relies on a very important assumption: that the file system overwrites data in place. This is the traditional way to do things, but many modern file system designs do not satisfy this
assumption.
...
* log-structured or journaled file systems, such as those supplied with
AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
...

Since the default for Linux is Ext3, or ReiserFS, shred is not actually overwriting on place.

Your tool to shred an entire disk using,
shred -u -n 30 /dev/hda
is a good one, however, format the disk to be EXT2 (non journalised) before you run the command.

TripleII

even journalized file systems in linux will not move a file to a different physical location on disk unless needed to allow for file size increase.

and the 4 k shown in Jack's example after shred hit the file is a minimum allocation for a file on any linux filesystem.

so, while shred relies on physical location to be effective, the journilized file systems do not move files around at every read / write operation.

Actually, I thought ext 3 was by default mounted as:

data=ordered

Which according to the clause of shred:

"In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to just metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount man page (man mount)."

This means that if the ext3 journaling mode is data=ordered or data=writeback, then shred works just as expected. From my understanding, ext3 is default as data=ordered.

If you do a man mount you can see what ordered means. It pushes all data out to the main filesystem prior to the metadata being committed to the journal.

So it depends on how you have your ext3 filesystem being mounted.

Is this what the author of Linux had in mind?A lot of typing?

Considering that you really need only the following:

$ shred -u private.txt

And that everything else is for the purpose of illustrating the example. Do you really find that a lot of typing?

Oh, and by the way, no matter how many time you click a file under windows, you won't shred it without 3rd party software. So unless you know something I don't, typing is better than nothing.

Lastly, before anyone calls me a zealot, I use bot windows and linux, thank you.

It is easy to configure a GUI file manager (e.g. Konqueror) to call shred on a set of files. So if point & click shredding is your (the readers) preference, it's easily available.

Someone inform the developer of the BALTHOR artificial intelligence project that BALTHOR has started repeating itself. This is the second time I've seen this exact formulation of a BALTHOR post on TR.

I've been using shred for a while, now.

Isn't that a shread?

From the man page:
-P Overwrite regular files before deleting them. Files are
overwritten three times, first with the byte pattern 0xff,
then 0x00, and then 0xff again, before they are deleted.
Specifying this flag for a read only file will cause rm to
generate an error message and exit. The file will not be
removed or overwritten.


Or is that just Unix????

Dan

The most indicated procedure is to backup regularly the sensitive files and folders.
It is mandatory.
The second is to have a supplimentary partition with the Windows XP/NT. Sorry! Please avoid to choose the NTFS organization. as consequence you can save files from Linux to a FAT-32 partition.
The third and the most important procedure is to have a wireless closed private network, transporting your strategic files to many nodes.
Yours faithfully,
Dan Gheorghe
http://dan.somnea.free.fr/2C/