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       If FILE is -, shred standard output.
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17       Mandatory arguments to long options are  mandatory  for  short  options
18       too.
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20       -f, --force
21              change permissions to allow writing if necessary
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23       -n, --iterations=N
24              overwrite N times instead of the default (3)
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26       --random-source=FILE
27              get random bytes from FILE
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29       -s, --size=N
30              shred this many bytes (suffixes like K, M, G accepted)
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32       -u     deallocate and remove file after overwriting
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34       --remove[=HOW]
35              like -u but give control on HOW to delete;  See below
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37       -v, --verbose
38              show progress
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40       -x, --exact
41              do not round file sizes up to the next full block;
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43              this is the default for non-regular files
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45       -z, --zero
46              add a final overwrite with zeros to hide shredding
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48       --help display this help and exit
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50       --version
51              output version information and exit
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53       Delete  FILE(s)  if  --remove (-u) is specified.  The default is not to
54       remove the files because it is common to operate on device  files  like
55       /dev/hda,  and those files usually should not be removed.  The optional
56       HOW parameter indicates how to remove a directory  entry:  'unlink'  =>
57       use  a  standard  unlink call.  'wipe' => also first obfuscate bytes in
58       the name.  'wipesync' => also sync each obfuscated byte to  disk.   The
59       default mode is 'wipesync', but note it can be expensive.
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61       CAUTION:  Note  that  shred relies on a very important assumption: that
62       the file system overwrites data in place.  This is the traditional  way
63       to  do  things, but many modern file system designs do not satisfy this
64       assumption.  The following are examples of file systems on which  shred
65       is not effective, or is not guaranteed to be effective in all file sys‐
66       tem modes:
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68       * log-structured or journaled file systems, such as those supplied with
69       AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
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71       *  file  systems  that  write  redundant data and carry on even if some
72       writes fail, such as RAID-based file systems
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74       * file systems that make snapshots, such  as  Network  Appliance's  NFS
75       server
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77       * file systems that cache in temporary locations, such as NFS version 3
78       clients
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80       * compressed file systems
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82       In the case of ext3 file systems, the  above  disclaimer  applies  (and
83       shred  is  thus  of  limited  effectiveness) only in data=journal mode,
84       which journals file data in addition to just  metadata.   In  both  the
85       data=ordered  (default) and data=writeback modes, shred works as usual.
86       Ext3 journaling modes can  be  changed  by  adding  the  data=something
87       option  to  the  mount  options  for  a  particular  file system in the
88       /etc/fstab file, as documented in the mount man page (man mount).
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90       In addition, file system backups and remote mirrors may contain  copies
91       of the file that cannot be removed, and that will allow a shredded file
92       to be recovered later.
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AUTHOR

95       Written by Colin Plumb.
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REPORTING BUGS

98       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
99       Report any translation bugs to <https://translationproject.org/team/>
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102       Copyright © 2019 Free Software Foundation, Inc.   License  GPLv3+:  GNU
103       GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
104       This  is  free  software:  you  are free to change and redistribute it.
105       There is NO WARRANTY, to the extent permitted by law.
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SEE ALSO

108       Full documentation <https://www.gnu.org/software/coreutils/shred>
109       or available locally via: info '(coreutils) shred invocation'
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113GNU coreutils 8.31                March 2019                          SHRED(1)
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