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.

       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 operat‐
       ing 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 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
       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-coreutils@gnu.org
       GNU coreutils home page: 
       General help using GNU software: 

COPYRIGHT
       Copyright  ©  2009  Free Software Foundation, Inc.  License GPLv3+: GNU
       GPL version 3 or later .
       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 7.4               September 2010                        SHRED(1)