OpenSolaris 2009.06 - man page for shred (opensolaris section 1)

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SHRED(1)				  User Commands 				 SHRED(1)

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

       shred [OPTIONS] FILE [...]

       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)

	      get random bytes from FILE (default /dev/urandom)

       -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

	      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

       CAUTION: Note that shred relies on a very important assumption: that the file system over-
       writes data in place.  This is the traditional way to do things, but many modern file sys-
       tem 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

       *  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 lim-
       ited 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.

       Written by Colin Plumb.

       Report bugs to <>.

       Copyright (C) 2006 Free Software Foundation, Inc.
       This  is free software.	You may redistribute copies of it under the terms of the GNU Gen-
       eral Public License <>.  There is NO WARRANTY, to  the
       extent permitted by law.

       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.

       See attributes(5) for descriptions of the following attributes:

       |Availability	    | SUNWgnu-coreutils  |
       |Interface Stability | Uncommitted	 |
       Source for GNU coreutils is available on

shred 6.7				  December 2006 				 SHRED(1)
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