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 [OPTION]... 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 (3)
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24       --random-source=FILE
25              get random bytes from FILE
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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[=HOW]
31              truncate and remove file after overwriting; See below
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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.  The optional
54       HOW parameter indicates how to remove a directory  entry:  'unlink'  =>
55       use  a  standard  unlink call.  'wipe' => also first obfuscate bytes in
56       the name.  'wipesync' => also sync each obfuscated byte to  disk.   The
57       default mode is 'wipesync', but note it can be expensive.
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59       CAUTION:  Note  that  shred relies on a very important assumption: that
60       the file system overwrites data in place.  This is the traditional  way
61       to  do  things, but many modern file system designs do not satisfy this
62       assumption.  The following are examples of file systems on which  shred
63       is not effective, or is not guaranteed to be effective in all file sys‐
64       tem modes:
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66       * log-structured or journaled file systems, such as those supplied with
67       AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
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69       *  file  systems  that  write  redundant data and carry on even if some
70       writes fail, such as RAID-based file systems
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72       * file systems that make snapshots, such  as  Network  Appliance's  NFS
73       server
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75       * file systems that cache in temporary locations, such as NFS version 3
76       clients
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78       * compressed file systems
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80       In the case of ext3 file systems, the  above  disclaimer  applies  (and
81       shred  is  thus  of  limited  effectiveness) only in data=journal mode,
82       which journals file data in addition to just  metadata.   In  both  the
83       data=ordered  (default) and data=writeback modes, shred works as usual.
84       Ext3 journaling modes can  be  changed  by  adding  the  data=something
85       option  to  the  mount  options  for  a  particular  file system in the
86       /etc/fstab file, as documented in the mount man page (man mount).
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88       In addition, file system backups and remote mirrors may contain  copies
89       of the file that cannot be removed, and that will allow a shredded file
90       to be recovered later.
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92       GNU  coreutils  online  help:  <http://www.gnu.org/software/coreutils/>
93       Report shred translation bugs to <http://translationproject.org/team/>
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AUTHOR

96       Written by Colin Plumb.
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99       Copyright  ©  2013  Free Software Foundation, Inc.  License GPLv3+: GNU
100       GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
101       This is free software: you are free  to  change  and  redistribute  it.
102       There is NO WARRANTY, to the extent permitted by law.
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SEE ALSO

105       The full documentation for shred is maintained as a Texinfo manual.  If
106       the info and shred programs are properly installed at  your  site,  the
107       command
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109              info coreutils 'shred invocation'
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111       should give you access to the complete manual.
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115GNU coreutils 8.22               October 2018                         SHRED(1)
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