https://performiq.com/kb/index.php?action=history&feed=atom&title=Securely_delete_files_with_shred 2026-05-18T23:15:46Z Revision history for this page on the wiki MediaWiki 1.37.1 https://performiq.com/kb/index.php?title=Securely_delete_files_with_shred&diff=4059&oldid=prev 2013-10-30T21:03:46Z

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PeterHarding https://performiq.com/kb/index.php?title=Securely_delete_files_with_shred&diff=1938&oldid=prev 2008-04-25T05:05:00Z

<p>New page: &lt;i&gt;by Vincent Danen, TechRepublic&lt;/i&gt; There are two utilities on a typical Linux box that can be used to delete files. Most users are familiar with the rm command. Most of the time, this...</p> <p><b>New page</b></p><div>&lt;i&gt;by Vincent Danen, TechRepublic&lt;/i&gt;<br /> <br /> <br /> There are two utilities on a typical Linux box that can be used to delete<br /> files. Most users are familiar with the rm command. Most of the time, this<br /> command is sufficient for routine deletion, but for files that contain<br /> sensitive data, you might need to scrub them so that they cannot be<br /> recovered later with other data retrieval tools.<br /> <br /> To delete files with sensitive content, rm is not sufficient. Instead,<br /> consider using the shred command, which not only deletes a file, but<br /> deletes it in such a way that it cannot be recovered. Shred overwrites the<br /> file multiple times with garbage prior to deleting it, ensuring that if<br /> anything does get retrieved, it isn&#039;t your top-secret data.<br /> <br /> &lt;pre&gt;<br /> For instance:<br /> <br /> $ echo &quot;this is private data&quot; &gt;private.txt<br /> <br /> $ cat private.txt<br /> <br /> this is private data<br /> <br /> $ ls -l private.txt<br /> <br /> -rw-r -- r-- 1 vdanen vdanen 21 Mar 4 09:36 private.txt<br /> &lt;/pre&gt;<br /> <br /> <br /> <br /> To illustrate how shred works, call it without any command-line options so<br /> that the garbage in the file can be viewed:<br /> <br /> &lt;pre&gt;<br /> $ shred private.txt<br /> <br /> $ cat private.txt<br /> <br /> ?9?-?w?K?=???l;b8SƉ?b???????@,?18!??DM??P?<br /> <br /> ...<br /> <br /> $ ls -l private.txt<br /> <br /> -rw-r -- r-- 1 vdanen vdanen 4096 Mar 4 09:36 private.txt<br /> &lt;/pre&gt;<br /> <br /> The rest of the output is removed as it is binary gibberish. You can also<br /> see the file size has changed.<br /> <br /> To delete the file after overwriting it with garbage, use the -u option.<br /> To see what shred is actually doing, give it the verbose -v option:<br /> <br /> &lt;pre&gt;<br /> $ shred -u -v private.txt<br /> <br /> shred: private.txt: pass 1/25 (random)...<br /> shred: private.txt: pass 2/25 (cccccc)...<br /> shred: private.txt: pass 3/25 (111111)...<br /> shred: private.txt: pass 4/25 (000000)...<br /> shred: private.txt: pass 5/25 (999999)...<br /> shred: private.txt: pass 6/25 (aaaaaa)...<br /> shred: private.txt: pass 7/25 (924924)...<br /> shred: private.txt: pass 8/25 (b6db6d)...<br /> shred: private.txt: pass 9/25 (6db6db)...<br /> shred: private.txt: pass 10/25 (888888)...<br /> shred: private.txt: pass 11/25 (492492)...<br /> shred: private.txt: pass 12/25 (db6db6)...<br /> shred: private.txt: pass 13/25 (random)...<br /> shred: private.txt: pass 14/25 (ffffff)...<br /> shred: private.txt: pass 15/25 (bbbbbb)...<br /> shred: private.txt: pass 16/25 (777777)...<br /> shred: private.txt: pass 17/25 (444444)...<br /> shred: private.txt: pass 18/25 (dddddd)...<br /> shred: private.txt: pass 19/25 (333333)...<br /> shred: private.txt: pass 20/25 (555555)...<br /> shred: private.txt: pass 21/25 (222222)...<br /> shred: private.txt: pass 22/25 (eeeeee)...<br /> shred: private.txt: pass 23/25 (666666)...<br /> shred: private.txt: pass 24/25 (249249)...<br /> shred: private.txt: pass 25/25 (random)...<br /> shred: private.txt: removing<br /> shred: private.txt: renamed to 00000000000<br /> shred: 00000000000: renamed to 0000000000<br /> shred: 0000000000: renamed to 000000000<br /> shred: 000000000: renamed to 00000000<br /> shred: 00000000: renamed to 0000000<br /> shred: 0000000: renamed to 000000<br /> shred: 000000: renamed to 00000<br /> shred: 00000: renamed to 0000<br /> shred: 0000: renamed to 000<br /> shred: 000: renamed to 00<br /> shred: 00: renamed to 0<br /> shred: private.txt: removed<br /> &lt;/pre&gt;<br /> <br /> As you can see, shred overwrites the file 25 times with garbage. After<br /> this, it renames the file 11 times before deleting it.<br /> <br /> Shred can also be used to overwrite entire disks instead of just files. If<br /> you wished to overwrite the contents of an entire hard drive, a process<br /> which would definitely take a fair amount of time, use:<br /> <br /> # shred -u -n 30 /dev/hda<br /> &lt;/pre&gt;<br /> <br /> This will overwrite the data on the drive with garbage using 30 passes.<br /> The drive will need to be re-formatted after this as even the filesystem<br /> structure will be destroyed.<br /> <br /> <br /> [[Category:Technet]]<br /> [[Category:Whitepages]]</div>

PeterHarding