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Instead of zeroing the filesystem, this command overwrites N times (default is 3) the disk content, making data recovery much harder.
The command accepts many more options
Make sure the file contents can't be retrieved if anyone gets ahold of your physical hard drive.
With hard drive partition:
gpg --default-recipient-self -o /path/to/encrypted_backup.gpg -e /dev/sdb1 && shred -z /dev/sdb1
WARNING/disclaimer: Be sure you... F&%k it--just don't try this.
This command remove a file from your filesystem like the normal rm command
but instead of deleting only the inode information this also delete the data that was stored on blocks
/!\ warning this may be long for large files
Instead, install apt-get install secure-delete and you can use:
-- srm to delete file and directory on hard disk
-- smem to delete file in RAM
-- sfill to delete "free space" on hard disk
-- sswap to delete all data from swap
This command securely erases all the unused blocks on a partition.
The unused blocks are the "free space" on the partition.
Some of these blocks will contain data from previously deleted files.
You might want to use this if you are given access to an old computer and you do not know its provenance.
The command could be used while booted from a LiveCD to clear freespace space on old HD.
On modern Linux LiveCDs, the "ntfs-3g" system provides ReadWrite access to NTFS partitions thus enabling this method to also be used on Wind'ohs drives.
NB depending on the size of the partition, this command could take a while to complete.
remove file that has sensitive info safely. Overwrites it 33 times with zeros
Shred can be used to shred a given partition or an complete disk. This should insure that not data is left on your disk
GNU shred is provided by the coreutils package on most Linux distribution (meaning, you probably have it installed already), and is capable of wiping a device to DoD standards.
You can give shred any file to destroy, be it your shell history or a block device file (/dev/hdX, for IDE hard drive X, for example). Shred will overwrite the target 25 times by default, but 3 is enough to prevent most recovery, and 7 passes is enough for the US Department of Defense. Use the -n flag to specify the number of passes, and man shred for even more secure erasing fun.
Note that shredding your shell history may not be terribly effective on devices with journaling filesystems, RAID copies or snapshot copies, but if you're wiping a single disk, none of that is a concern. Also, it takes quite a while :)