SHRED(1) User Commands SHRED(1)
NAME
shred - overwrite a file to hide its contents, and optionally delete it
SYNOPSIS
shred [OPTION]... FILE...
DESCRIPTION
Overwrite the specified FILE(s) repeatedly, in order to make it harder for even very expensive hardware prob‐
ing 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 (3)
--random-source=FILE
get random bytes from FILE
-s, --size=N
shred this many bytes (suffixes like K, M, G accepted)
-u, --remove[=HOW]
truncate and remove file after overwriting; See below
-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 remove the files because it is common to
operate on device files like /dev/hda, and those files usually should not be removed. The optional HOW param‐
eter indicates how to remove a directory entry: 'unlink' => use a standard unlink call. 'wipe' => also first
obfuscate bytes in the name. 'wipesync' => also sync each obfuscated byte to disk. The default mode is
'wipesync', but note it can be expensive.
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 effec‐
tive in all file system modes:
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.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report shred translation bugs to
<http://translationproject.org/team/>
AUTHOR
Written by Colin Plumb.
COPYRIGHT
Copyright © 2013 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 per‐
mitted by law.
SEE ALSO
The full documentation for shred is maintained as a Texinfo manual. If the info and shred programs are prop‐
erly installed at your site, the command
info coreutils 'shred invocation'
should give you access to the complete manual.
GNU coreutils 8.22 November 2016 SHRED(1)
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