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-coreutils@gnu.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 © 2011 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.
 

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