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NAME | SYNOPSIS | DESCRIPTION | AUTHOR | REPORTING BUGS | COPYRIGHT | SEE ALSO | COLOPHON |
SHRED(1) User Commands SHRED(1)
shred - overwrite a file to hide its contents, and optionally delete
it
shred [OPTION]... FILE...
Overwrite the specified FILE(s) repeatedly, in order to make it
harder for even very expensive hardware probing to recover the data.
If FILE is -, shred standard output.
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 truncate and remove file after overwriting
--remove[=HOW]
like -u but give control on HOW to delete; 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
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 parameter 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 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.
Written by Colin Plumb.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report shred translation bugs to
<http://translationproject.org/team/>
Copyright © 2017 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.
Full documentation at: <http://www.gnu.org/software/coreutils/shred>
or available locally via: info '(coreutils) shred invocation'
This page is part of the coreutils (basic file, shell and text
manipulation utilities) project. Information about the project can
be found at ⟨http://www.gnu.org/software/coreutils/⟩. If you have a
bug report for this manual page, see
⟨http://www.gnu.org/software/coreutils/⟩. This page was obtained from
the tarball coreutils-8.27.tar.xz fetched from
⟨http://www.gnutls.org/download.html⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
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you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
GNU coreutils 8.27 March 2017 SHRED(1)
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