- Boot using your favorite linux. Ubuntu Knoppix Debian
- If you have multiple disks, check twice: fdisk -l
- Stop using the disk: umount /dev/sdi1
- Read the caution (below) and in the man page: man shred
- Shred it only one time, and fill with zeros: shred -n1 -v -z /dev/sdi
Darik's Boot And Nuke
# fdisk -l Disk /dev/sdi: 10.2 GB, 10248118272 bytes 255 heads, 63 sectors/track, 1245 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x9da19da1 Device Boot Start End Blocks Id System /dev/sdi1 * 1 1244 9992398+ 7 HPFS/NTFS Write one pass of random data to the entire disk, then erase it by writing zeros: shred -n1 -v -z /dev/sdi The same thing works on individual files: # shred -n9 -v -z Junk.txt shred: Junk.txt: pass 1/10 (random)... shred: Junk.txt: pass 2/10 (555555)... shred: Junk.txt: pass 3/10 (000000)... shred: Junk.txt: pass 4/10 (6db6db)... shred: Junk.txt: pass 5/10 (random)... shred: Junk.txt: pass 6/10 (ffffff)... shred: Junk.txt: pass 7/10 (492492)... shred: Junk.txt: pass 8/10 (aaaaaa)... shred: Junk.txt: pass 9/10 (random)... shred: Junk.txt: pass 10/10 (000000)... CAUTION: Note that shred relies on a very important assumption: that the file system overwrites data in place. This is the traditional way to do things, but many modern file system designs do not satisfy this assumption. The following are examples of file systems on which shred is not effective, or is not guaranteed to be effective in all file system modes: * log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.) * file systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems * file systems that make snapshots, such as Network Appliance's NFS server * file systems that cache in temporary locations, such as NFS version 3 clients * compressed file systems In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to just metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount man page (man mount). In addition, file system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file to be recovered later.
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