The following patches make the shred man page and doc/coreutils.texi
documentation on shred more specific, to reflect the fact that shred
should, in fact, work normally in all ext3 journaling modes except
data=journal mode. Previous documentation gave the impression that
that shred was ineffective on ext3, period.
Thanks for any feedback,
Mark Melahn
shred.c patch
@@ -193,7 +193,7 @@
that the filesystem overwrites data in place. This is the traditional\n\
way to do things, but many modern filesystem designs do not satisfy this\n\
assumption. The following are examples of filesystems on which shred is\n\
-not effective:\n\
+not effective, or is not guaranteed to be effective in all filesystem modes:\n\
\n\
), stdout);
fputs (_(\
@@ -212,6 +212,14 @@
\n\
* compressed filesystems\n\
\n\
+In the case of ext3 filesystems, the above disclaimer applies\n\
+(and shred is thus of limited effectiveness) only in data=journal mode,\n\
+which journals file data in addition to just metadata. In both the\n\
+data=ordered (default) and data=writeback modes, shred works as usual.\n\
+Ext3 journaling modes can be changed by adding the data=something option\n\
+to the mount options for a particular file system in the /etc/fstab file,\n\
+as documented in the mount man page (man mount).\n\
+\n\
In addition, file system backups and remote mirrors may contain copies\n\
of the file that cannot be removed, and that will allow a shredded file\n\
to be recovered later.\n\
end shred.c patch
doc/coreutils.texi patch
@@ -6967,7 +6967,7 @@
@item
Log-structured or journaled filesystems, such as those supplied with
-AIX and Solaris, and JFS, ReiserFS, XFS, Ext3, etc.
+AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in data=journal mode), etc.
@item
Filesystems that write redundant data and carry on even if some writes
@@ -6984,6 +6984,8 @@
Compressed filesystems.
@end itemize
+In the particular case of ext3 filesystems, the above disclaimer
applies (and @command{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,
@command{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).
+
If you are not sure how your filesystem operates, then you should assume
that it does not overwrite data in place, which means that shred cannot
reliably operate on regular files in your filesystem.
end doc/coreutils.texi patch
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