[SOLVED] erase unused space

l0rddarkf0rce · 04-18-2015, 04:52 PM

Hello all...

Is there a way to securely erase the unused space from the HD that I currently have Slackware on (/dev/sda in my case)?

jmccue · 04-18-2015, 05:45 PM

Try

Code:

dd of=x if=/dev/urandom bs=4096

It will fill up you disk so maybe best to execute it in single use mode. Once complete delete the file after a sync(1)

John VV · 04-18-2015, 07:33 PM

the above is the easiest
and it is built in

but if you have to have a program

install "bleachbit"
and use the gtk based gui

Gerard Lally · 04-18-2015, 07:42 PM

Quote:

Originally Posted by jmccue

Try

Code:

dd of=x if=/dev/urandom bs=4096

It will fill up you disk so maybe best to execute it in single use mode. Once complete delete the file after a sync(1)

I don't think this would fill the free space with random data across multiple partitions. Or am I wrong?

metaschima · 04-18-2015, 08:19 PM

Quote:

Originally Posted by gezley

I don't think this would fill the free space with random data across multiple partitions. Or am I wrong?

You would have to do it for each partition.

/dev/urandom is slow, but secure. You could also use /dev/zero instead, it is faster, but in extreme circumstances is less secure (very high tech microscope recovery techniques that have never been used in practice and aren't practical either).

STDOUBT · 04-18-2015, 08:37 PM

dd of=x if=/dev/urandom bs=4096

The above would NOT preserve any data, where 'x'= a partition.
Pretty sure l0rddarkf0rce just wants to erase unallocated disk space

descendant_command · 04-18-2015, 08:55 PM

Quote:

Originally Posted by STDOUBT

dd of=x if=/dev/urandom bs=4096

The above would NOT preserve any data, where 'x'= a partition.
Pretty sure l0rddarkf0rce just wants to erase unallocated disk space

Yeah, but as written (where x is a file) it will do exactly that.

l0rddarkf0rce · 04-18-2015, 11:15 PM

Quote:

Originally Posted by descendant_command

Quote:

Originally Posted by STDOUBT

dd of=x if=/dev/urandom bs=4096

The above would NOT preserve any data, where 'x'= a partition.
Pretty sure l0rddarkf0rce just wants to erase unallocated disk space

Yeah, but as written (where x is a file) it will do exactly that.

Both correct. I went with /dev/zero not as secure but good enough for my purposes. I guess that my Slackware box will be out of commission for several more hours filling the available 250GB on the partition will take a while.

kikinovak · 04-19-2015, 02:01 AM

Quote:

Originally Posted by l0rddarkf0rce

Hello all...

Is there a way to securely erase the unused space from the HD that I currently have Slackware on (/dev/sda in my case)?

I'm not sure if I understand you correctly.

Sometimes I test-drive systems not in a virtual environment, but on a real machine here in my office. I'm using Ghost for Linux (G4L) to make backups to a local FTP server. Before doing that, I zero out the unused space on the hard disks, to reduce the size of the compressed images. Here's how I do that:

Code:

# dd if=/dev/zero of=/0bits bs=20M ; rm -f /0bits

Cheers,

Niki

speck · 04-19-2015, 02:46 AM

I hope the meaning of "unallocated" is agreed upon by all, hopefully he didn't just write over a partition that contained some (allocated) data he wanted to retain.

kikinovak · 04-19-2015, 03:13 AM

Quote:

Originally Posted by STDOUBT

dd of=x if=/dev/urandom bs=4096

The above would NOT preserve any data, where 'x'= a partition.
Pretty sure l0rddarkf0rce just wants to erase unallocated disk space

If we don't hear from him anymore, he's probably followed the advice above.

l0rddarkf0rce · 04-19-2015, 12:19 PM

Quote:

Originally Posted by kikinovak

If we don't hear from him anymore, he's probably followed the advice above.

Yes I meant unallocated space and yes x := a file. Many thanks to all!

John VV · 04-19-2015, 07:23 PM

this discussion is why i post that dd solution as

Code:

dd of=/OneBigFile.bin if=/dev/zero

and leave the bs as the default 512

just adjust for the partitions

Code:

dd of=/dev/sdb1/OneBigFile.bin if=/dev/zero

rknichols · 04-19-2015, 08:50 PM

Quote:

Originally Posted by John VV

just adjust for the partitions

Code:

dd of=/dev/sdb1/OneBigFile.bin if=/dev/zero

Ummm, that's going to create an ordinary file in /dev and fill up your devfs or devtmpfs in memory, leaving the actual filesystem on /dev/sdb1 untouched.

[EDIT] Make that "try to create". It will, fortunately, fail since /dev/sdb1 is not a directory.

gus3 · 04-20-2015, 03:52 PM

Fill the partition with a file, using /dev/zero, then shred the file:

Code:

# dd if=/dev/zero of=zeros
# shred -vu zeros

Of course, probably not necessary on SSD storage. In that case, you would want to

Code:

# dd if=/dev/zero of=zeros
# rm zeros
# fstrim -v /mount/point