1SHRED(1)                         User Commands                        SHRED(1)
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NAME

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

9       shred [OPTIONS] FILE [...]
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DESCRIPTION

12       Overwrite  the specified FILE(s) repeatedly, in order to make it harder
13       for even very expensive hardware probing to recover the data.
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15       Mandatory arguments to long options are  mandatory  for  short  options
16       too.
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18       -f, --force
19              change permissions to allow writing if necessary
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21       -n, --iterations=N
22              Overwrite N times instead of the default (25)
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24       --random-source=FILE
25              get random bytes from FILE (default /dev/urandom)
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27       -s, --size=N
28              shred this many bytes (suffixes like K, M, G accepted)
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30       -u, --remove
31              truncate and remove file after overwriting
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33       -v, --verbose
34              show progress
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36       -x, --exact
37              do not round file sizes up to the next full block;
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39              this is the default for non-regular files
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41       -z, --zero
42              add a final overwrite with zeros to hide shredding
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44       --help display this help and exit
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46       --version
47              output version information and exit
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49       If FILE is -, shred standard output.
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51       Delete  FILE(s)  if  --remove (-u) is specified.  The default is not to
52       remove the files because it is common to operate on device  files  like
53       /dev/hda,  and those files usually should not be removed.  When operat‐
54       ing on regular files, most people use the --remove option.
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56       CAUTION: Note that shred relies on a very  important  assumption:  that
57       the  file system overwrites data in place.  This is the traditional way
58       to do things, but many modern file system designs do not  satisfy  this
59       assumption.   The following are examples of file systems on which shred
60       is not effective, or is not guaranteed to be effective in all file sys‐
61       tem modes:
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63       * log-structured or journaled file systems, such as those supplied with
64       AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
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66       * file systems that write redundant data and  carry  on  even  if  some
67       writes fail, such as RAID-based file systems
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69       *  file  systems  that  make snapshots, such as Network Appliance's NFS
70       server
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72       * file systems that cache in temporary locations, such as NFS version 3
73       clients
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75       * compressed file systems
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77       In  the  case  of  ext3 file systems, the above disclaimer applies (and
78       shred is thus of limited  effectiveness)  only  in  data=journal  mode,
79       which  journals  file  data  in addition to just metadata.  In both the
80       data=ordered (default) and data=writeback modes, shred works as  usual.
81       Ext3  journaling  modes  can  be  changed  by adding the data=something
82       option to the mount  options  for  a  particular  file  system  in  the
83       /etc/fstab file, as documented in the mount man page (man mount).
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85       In  addition, file system backups and remote mirrors may contain copies
86       of the file that cannot be removed, and that will allow a shredded file
87       to be recovered later.
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AUTHOR

90       Written by Colin Plumb.
91

REPORTING BUGS

93       Report bugs to <bug-coreutils@gnu.org>.
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96       Copyright © 2007 Free Software Foundation, Inc.
97       This  is  free  software.   You may redistribute copies of it under the
98       terms      of      the      GNU      General       Public       License
99       <http://www.gnu.org/licenses/gpl.html>.   There  is NO WARRANTY, to the
100       extent permitted by law.
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SEE ALSO

103       The full documentation for shred is maintained as a Texinfo manual.  If
104       the  info  and  shred programs are properly installed at your site, the
105       command
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107              info shred
108
109       should give you access to the complete manual.
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113GNU coreutils 6.9                 March 2008                          SHRED(1)
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