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.
Mandatory arguments to long options are mandatory for short options too.
change permissions to allow writing if necessary
overwrite N times instead of the default (3)
get random bytes from FILE
shred this many bytes (suffixes like K, M, G accepted)
truncate and remove file after overwriting
do not round file sizes up to the next full block;
this is the default for non-regular files
add a final overwrite with zeros to hide shredding
--help display this help and exit
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. When operating on regular files, most people use the --remove
CAUTION: Note that shred relies on a very important assumption: that the file system over-
writes data in place. This is the traditional way to do things, but many modern file sys-
tem 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
* 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 lim-
ited 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.
Report shred bugs to firstname.lastname@example.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>
Report shred translation bugs to <http://translationproject.org/team/>
Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or
This is free software: you are free to change and redistribute it. There is NO WARRANTY,
to the extent permitted by law.
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.
GNU coreutils 8.5 February 2011 SHRED(1)