shred(1)

NAME

       shred - overwrite a file to hide its contents, and optionally delete it

SYNOPSIS

       shred [OPTIONS] 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 (25)

       -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 bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2005 Free Software Foundation, Inc.
       This  is  free  software.   You may redistribute copies of it under the
       terms      of      the      GNU      General       Public       License
       <http://www.gnu.org/licenses/gpl.html>.   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 shred

       should give you access to the complete manual.

shred 5.93                       November 2005                        SHRED(1)