shred

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.

       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     deallocate 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 sys-
       tem 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  op-
       tion  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
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report shred translation bugs to <https://translationproject.org/team/>

COPYRIGHT
       Copyright (C) 2018 Free Software Foundation, Inc.  License GPLv3+:  GNU
       GPL version 3 or later <https://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
       Full documentation at: <https://www.gnu.org/software/coreutils/shred>
       or available locally via: info '(coreutils) shred invocation'

GNU coreutils 8.30              September 2019                        SHRED(1)