SHRED(1) GNU coreutils 6.12 SHRED(1)
User Commands User Commands
June 2008
NAME
shred - overwrite a file to hide its contents, and optionally delete
it
SYNOPSIS
shred [OPTIONS] FILE [...]
DESCRIPTION
Overwrite the specified FILE(s) repeatedly, in order to make it harder
for even very expensive hardware probing to recover the data.
Mandatory arguments to long options are mandatory for short options
too.
-f, --force
change permissions to allow writing if necessary
-n, --iterations=N
Overwrite N times instead of the default (25)
--random-source=FILE
get random bytes from FILE (default /dev/urandom)
-s, --size=N
shred this many bytes (suffixes like K, M, G accepted)
-u, --remove
truncate and remove file after overwriting
-v, --verbose
show progress
-x, --exact
do not round file sizes up to the next full block;
this is the default for non-regular files
-z, --zero
add a final overwrite with zeros to hide shredding
--help
display this help and exit
--version
output version information and exit
If FILE is -, shred standard output.
Delete FILE(s) if --remove (-u) is specified. The default is not to
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SHRED(1) GNU coreutils 6.12 SHRED(1)
User Commands User Commands
June 2008
remove the files because it is common to operate on device files like
/dev/hda, and those files usually should not be removed. When
operating on regular files, most people use the --remove option.
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. The following are examples of file systems on which shred
is not effective, or is not guaranteed to be effective in all file
system modes:
* log-structured or journaled file systems, such as those supplied
with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
* file systems that write redundant data and carry on even if some
writes fail, such as RAID-based file systems
* file systems that make snapshots, such as Network Appliance's NFS
server
* file systems that cache in temporary locations, such as NFS version
3 clients
* compressed file systems
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).
In addition, file system backups and remote mirrors may contain copies
of the file that cannot be removed, and that will allow a shredded
file to be recovered later.
AUTHOR
Written by Colin Plumb.
REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>.
COPYRIGHT
Copyright c 2008 Free Software Foundation, Inc. License GPLv3+: GNU
GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
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SHRED(1) GNU coreutils 6.12 SHRED(1)
User Commands User Commands
June 2008
SEE ALSO
The full documentation for shred is maintained as a Texinfo manual.
If the info and shred programs are properly installed at your site,
the command
info coreutils 'shred invocation'
should give you access to the complete manual.
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