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how to delete a file permanently from computer

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Top Forums Programming how to delete a file permanently from computer
# 8  
Old 08-25-2009
'deleting' a file
A file is not deleted until it has been overwritten on the disk (at least 3 times) with other data. Otherwise, the information still exists on the system, its space on the disk is simply flagged as available by the OS. Over time, the contents of the file are overwritten by other applications, but the time interval is unpredictable.

To ensure that information is destroyed and cannot be accessed via forensic methods, you simply rewind the file and fill it with garbage and close it. Then open, write garbage, close. It is necessary to ensure that the actual disk sectors that map to the file are written to, not simply the disk cache in memory.

Unless you are working for a security agency, financial institution or some such, simply deleting the file should be enough.

There are software packages out there that will wipe a disk clean, but if you are discarding a computer and you have sensitive information on a disk, removing the drive(s) and taking a sledgehammer to it also works.
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LEARN ABOUT OPENSOLARIS

sun

machid(1)							   User Commands							 machid(1)

NAME

       machid, sun, iAPX286, i286, i386, i486, i860, pdp11, sparc, u3b, u3b2, u3b5, u3b15, vax, u370 - get processor type truth value

SYNOPSIS

       sun

       iAPX286

       i386

       pdp11

       sparc

       u3b

       u3b2

       u3b5

       u3b15

       vax

       u370

DESCRIPTION

       The following commands will return a true value (exit code of 0) if you are using an instruction set that the command name indicates.

       sun	  True if you are on a Sun system.

       iAPX286	  True if you are on a computer using an iAPX286 processor.

       i386	  True if you are on a computer using an iAPX386 processor.

       pdp11	   True if you are on a PDP-11/45tm or PDP-11/70tm.

       sparc	  True if you are on a computer using a SPARC-family processor.

       u3b	  True if you are on a 3B20 computer.

       u3b2	  True if you are on a 3B2 computer.

       u3b5	  True if you are on a 3B5 computer.

       u3b15	  True if you are on a 3B15 computer.

       vax	  True if you are on a VAX-11/750tm or VAX-11/780tm.

       u370	  True if you are on an IBM(R) System/370tm computer.

       The  commands  that  do	not  apply will return a false (non-zero) value. These commands are often used within makefiles (see make(1S)) and
       shell scripts (see sh(1)) to increase portability.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       make(1S), sh(1), test(1), true(1), uname(1), attributes(5)

NOTES

       The machid family of commands is obsolete. Use uname -p and uname -m instead.

SunOS 5.11							    5 Jul 1990								 machid(1)