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So if you want to erase a drive with custom data you can do yes "text here" > /dev/sdX but I was wondering if this is a secure way to do so?

dsadsads
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  • I really have to wonder the reason for specifying the data to be written to the device. It would be much more secure to use shred. Writing data using yes would probably be pretty secure, but shred's three passes on the drive would be better. – MetaNova Jun 21 '14 at 17:01

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Not directly, I guess, but possible.

running this:

sudo yes "ruslansendthistothedisk1gb" > /dev/sdb

I got 

bash: /dev/sdb: Permission denied

Then I decided to it with dd:

yes "ruslansendthistothedisk1gb" > file.txt

and 

sudo dd if=file.txt of=/dev/sdb

this worked:

167424+0 records in
167424+0 records out
85721088 bytes (86 MB) copied, 27.073 s, 3.2 MB/s

As for being secure, I only thought what if you send data with size more than a device capability, would not it be damaging anything else.

Then I decided to feed the device with file which is knowingly more than my /dev/sdb disk.

sudo fdisk -l /dev/sdb

as can be seen size is 1015808000 byte

Disk /dev/sdb: 1015 MB, 1015808000 bytes 32 heads, 61 sectors/track, 1016 cylinders, total 1984000 sectors  
Units = sectors of 1 * 512 = 512 bytes 
Sector size (logical/physical): 512 bytes / 512 bytes  
I/O size (minimum/optimal): 512 bytes / 512 bytes  
Disk identifier: 0x6874646e
Disk /dev/sdb doesn't contain a valid partition table

the file size:

ls -la file.txt

as can be seen is 1103699968

-rw-rw-r-- 1 shiva shiva 1103699968 Jun 21 15:00 file.txt

and copy it to the device:

sudo dd if=file.txt of=/dev/sdb

after several minutes it said:

dd: writing to `/dev/sdb': No space left on devicel

and in short time

1984001+0 records in
1984000+0 records out
1015808000 bytes (1.0 GB) copied, 451.234 s, 2.3 MB/s

As it can be seen, partition disappeared even after copying short fragment to the device, I assume it is enough to send just one random byte to destroy file system and it will not show partition, but still can be dumped by dd. So if you want do erase all your device with no chance to find any data on it, then it is better to "overwrite" it completely, with full size of the device.

Ruslan Gerasimov
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  • If you run sudo yes "text" > /dev/sdb or just run it as root, it works. I was wondering about the security of it. – dsadsads Jun 21 '14 at 14:35
  • I did try to run it with sudo it gave bash: /dev/sdb: Permission denied, I did not try as root. – Ruslan Gerasimov Jun 21 '14 at 22:20
  • Odd, just sudo works great for me. I was just curious about this as a funny way to erase something so if anyone ever tried recovery they would get a good laugh.

    For true security, I would zero it and then yes "stuff" > /dev/sdX

     – dsadsads Jun 22 '14 at 01:54