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 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 (3)

       --random-source=FILE
              get random bytes from FILE

       -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 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 shred bugs to bug-coreutilsATgnu.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
       Copyright   (C)   2010   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.

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.



GNU coreutils 8.5                                         November 2010                                                 SHRED(1)