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Full Discussion: shred multiple options
Top Forums UNIX for Advanced & Expert Users shred multiple options Post 302333324 by codecellar on Sunday 12th of July 2009 03:15:55 PM
Old 07-12-2009
shred multiple options
I've created a wxpython gui for the shred command. I can successfully mix and match all the shred options except two: -size and --random-source. (Man page definitions below). -size and --random-source seem to only work when they are used as the sole option passed.

For example,

I can zero a file fine with this:

Code:
shred -z mySecretFile.txt

I can use a random source fine with this:

Code:
shred --random-source=myRandomData mySecretFile.txt

But, if I want to do both:

Code:
shred -z --random-source=myRandomData mySecretFile.txt

or, zero and use the size option

Code:
shred -z --size=1000 mySecretFile.txt

shred with not perform what I'm intending it to do.

Anyone know the syntax necessary to use -size and -random-source options along with the others?

From the man page:

Code:
-f, --force
              change permissions to allow writing if necessary

       -n, --iterations=N
              Overwrite N times instead of the default (25)

       --random-source=FILE
              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

 

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LEARN ABOUT X11R4

shred

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.

       If FILE is -, shred standard output.

       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     truncate and remove file after overwriting

       --remove[=HOW]
	      like -u but give control on HOW to delete;  See below

       -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

       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.  The optional HOW parameter indicates how to remove a directory entry: 'unlink' =>
       use  a standard unlink call.  'wipe' => also first obfuscate bytes in the name.	'wipesync' => also sync each obfuscated byte to disk.  The
       default mode is 'wipesync', but note it can be expensive.

       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

       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report shred translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2017 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

       Full documentation at: <http://www.gnu.org/software/coreutils/shred>
       or available locally via: info '(coreutils) shred invocation'

GNU coreutils 8.28						   January 2018 							  SHRED(1)
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