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there is the whole recovery applications and commands . I actually need to delete some sensitive data permanently so nobody can access it anymore , no matter what application they use or commands they carry on , any help ??

Abdullah R. Ghareeb
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  • This isn't really ubuntu specific, but what you'll need to do is a multi-pass format which overwrites the drive with random data. –  Feb 24 '17 at 04:22
  • Here's a pretty robust guide: http://lifehacker.com/5153684/properly-erase-your-physical-media –  Feb 24 '17 at 04:25
  • Remove your hard drive, put some thermite on it and set it on fire to melt the hard drive platters for good. ;-] Wear some protective gear (hands, eyes/face, chest) like the guy at the bottom of this blog post. – David Foerster Feb 24 '17 at 07:47

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There is no completely safe method except to destroy the hard disk drive completely (physically). But for most cases it should be enough to use DBAN to overwrite the drive.

You have to make a fresh installation after that, and you may want to use 'encrypted disk' alias LVM with encryption. An encrypted system is difficult to recover, so please back it up at regular intervals, and use a good passphrase, that you can remember, but other people cannot guess.

sudodus
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See the shred command (and its man page for more info). For example, this truncates, overwrites, and then removes a file called writing.txt:

shred -uvz writing.txt

Update: Thanks to Andrius for the comment about modern filesystems. According to the GNU page on shred, the utility makes some assumptions about how filesystems work, and modern filesystems that use journaling could be problematic for shred. The GNU page notes, as a workaround, that it is probably more secure to use shred to shred a device, but even this is not a guarantee. Read more here:

https://www.gnu.org/software/coreutils/manual/html_node/shred-invocation.html

The EFF has a how-to page, with some additional information, on using BleachBit to securely delete data on Linux:

https://ssd.eff.org/en/module/how-delete-your-data-securely-linux

Sean Burns
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  • shred doesn't work with modern filesystems. They simply write data to another place on disk (copy on write). So you will be just writing zeroes somewhere else without overwriting file. – Andrius Štikonas Feb 24 '17 at 11:43