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securely erase unused blocks in a partition

Terminal - securely erase unused blocks in a partition
# cd $partition; dd if=/dev/zero of=ShredUnusedBlocks bs=512M; shred -vzu ShredUnusedBlocks
2009-06-21 14:17:22
User: mpb
Functions: cd dd shred
8
securely erase unused blocks in a partition

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.

Alternatives

There are 5 alternatives - vote for the best!

Terminal - Alternatives

Know a better way?

If you can do better, submit your command here.

What others think

It looks like you forgot to specify the 'dd' part before if=/dev/zero. Also, be careful when running this on the partition where /home or /tmp is mounted because it can cause weird hangups when applications can no longer create temporary files, like when starting an X session.

Comment by bwoodacre 378 weeks and 6 days ago

@bwoodacre

Thanks for pointing out the missing "dd". Fixed now.

You are also right about needing to be careful about filling /tmp. Hence the mention of LiveCD.

Comment by mpb 378 weeks and 6 days ago

Doesn't handle slack in the last block of a file. Also other space is probably not overwritten on journalling filesystems.

Comment by pixelbeat 378 weeks and 5 days ago

fwiw dban linux is supposed to be the ultimate shredder...

Comment by linuxrawkstar 378 weeks and 5 days ago

Good point pixelbeat. In more words: in some filesystems, a 10 byte file still takes up (say, for instance) 4069 bytes (4K) of physical disk space. If you want to leave the existing files on the filesystem untouched, then this slack space is unwritable at the filesystem level. Something like ext2 would behave this way, but reiser3 packs many small files into the same block. So expanding a giant file and shredding it is a great start if you want/need to do things in place, but you aren't guaranteed to shred 100% of the unused disk bytes unless you use something at the block-device level like dban.

Comment by bwoodacre 378 weeks and 5 days ago

@pixelbeat

Where is the slack?

The "dd" creates a single file from all the unused blocks in the partition in a file called "ShredUnusedBlocks".

So the end of this file is the end of the last unused block.

You can use the "df" command after the "dd" to verify 100% of the space in the partition is used up when the "ShredUnusedBlocks" file is created.

Regarding the journal, what do you think the journal will be full of? I think it will be mostly full of writes of random data from the shred command. If the default number of overwrites from shred is not considered enough, it can be increased with the "-n" (or "--iterations=n") option.

Example: specifying "-n16" for 16 iterations:

cd /boot; dd if=/dev/zero of=ShredUnusedBlocks bs=512M; shred -vzu -n16 ShredUnusedBlocks

Comment by mpb 378 weeks and 4 days ago

2016-6-7 leilei

"Tweed is an excellent fabric especially when you are living in place like London. London is known for its cold weather and in such climate, tweed works absolutely fine. One of the biggest advantages of buying a tweed suit is that you it can be worn all together or can be incorporated separately into pieces in your wardrobe. Tweed suits in London is quite famous amongst men. So let us understand, what exactly tweed fabric is.

What is Tweed?

Tweed is a warm rough to touch fabric and was originated in Scotland. The reason why tweed suits in London are famous is because of its loose weave which makes it flexible and comfortable during winters. The tweed fabric is referred to the weave of fabric; therefore when you see different kinds of tweed, it would tell you the pattern it has been woven. One of the most popular kinds of tweed is the herringbone tweed which a diagonally v-shaped black and white weave. The herringbone tweed gives a rich visual texture and known for its versatility.

Ways to wear Tweed in winters

Everybody needs to wear warm clothes during the winter month to protect from the chilly weather outside. However, many people think that they might have to compromise fashion during those chilly months. Not now! There are many fabrics that you can use to protect yourself from the weather as well as still enjoy great looks. Tweed is one of the fabrics that can make you awesome even in winters as well. Below are some ways of how you can incorporate tweed with other pieces in your wardrobe

"

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"Casually ? if you are a starter with tweed then it is recommended to start with plain variety of tweed. You can wear a tweed jacket with dark blue jeans and high boots. Incorporate a neutral t-shirt or a winter shirt under the jacket.

At work ? Tweed suit in London are quite popular as one of the formal attires. Heavy woven tweeds can make you look older, so try buying tweed suits in London that are finely weaved and pair it with your regular shirts like white or blue with smart formal shoes. Believe it or not, it can win you praise at work.

Accessorise ? Apart from wearing tweed suits in London as attire you can even use accessories made out of tweed. Tweed caps, laptop bags, scarves, gloves are a smart way to incorporate tweed in your winter collection. It is also a safe way of using tweed fabric if you are not too comfortable wearing it. There is even footwear that has tweed as their centre fabric and looks awesome.

Taking care of Tweed

Though the fabric boasts itself about being tough and rugged, it still requires a good care to use it for coming years as well. Due to its weave structure it often pick up dirt and stains that can get hard to remove. Make sure you take your tweed clothes for dry cleaning as washing them in washing machines can make them shrink. Also, keep them in cool dry place so that they do not get attracted by moths.

"

Comment by leilei3915 15 weeks and 5 days ago

Your point of view

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