The special file corresponding to an entire disk is scrubbed and all data on it is destroyed. This mode is selected if file is a character or block special file. This is the most effective method.
A regular file is scrubbed and only the data in the file (and optionally its name in the directory entry) is destroyed. The file size is rounded up to fill out the last file system block. This mode is selected if file is a regular file.
A file is created, expanded until the file system is full, then scrubbed as in item 2. This mode is selected with the -X option.
Scrub implements user-selectable pattern algorithms that are compliant with DoD 5520.22-M or NNSA NAP-14.x.
Install Scrub in Ubuntu
First you need to install Alien
sudo apt-get install alien
This will help us to convert .rpm files in to .deb packages
Now you need to download the Scrub latest version from here
You have scrub-1.8-1.i386.rpm file now.Convert this file in to .deb using the following command
sudo alien -k scrub-1.8-1.i386.rpm
Now you have the scrub-1.8-1.i386.deb package.You need to install this package using the following command
sudo dpkg -i scrub-1.8-1.i386.deb
This will complete the installation
Create a scratch directory for scrub.
sudo mkdir /scratch
scrub [-f] [-p nnsa|dod|bsi] [-X] [-D newname] [-s size] file
sudo scrub -X /scratch/junk
Delete junk file once scrub is finished.
sudo rm -f /scratch/junk
Check this forum post