Inquiry:How to totally wipe out the entire hard drive

Dear All

Can you please let me know how can I totally wipe out the entire of my hard drive under Debian OS ?

Thank you in advance

Regards

H.Motamedi

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Follow-Ups:
- Re: Inquiry:How to totally wipe out the entire hard drive
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- Re: Inquiry:How to totally wipe out the entire hard drive
  - From: Tzafrir Cohen <tzafrir@cohens.org.il>
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  - From: Osamu Aoki <osamu@debian.org>
- Re: Inquiry:How to totally wipe out the entire hard drive
  - From: "Andrew M.A. Cater" <amacater@galactic.demon.co.uk>