As others have mentioned, not a good idea to do this from a drive in use.
There's a couple problems. Binaries are loaded into memory as the execution
hit's an address that's on disk and not in memory, called a page fault.
So sshd for instance when runs will generate a bunch of page faults, but those
pages in memory can be paged out if needed for something else. So say you are
happily wiping your disk, a new ssh connection is attempted from some network
scan. It might trigger a page fault, if that page doesn't exist on disk it
might well crash, which might well terminate your connection and your disk would
be partially wiped AND likely not bootable.
After your dd you might want to use hdarm --security-erase explained at:
https://grok.lsu.edu/article.aspx?articleid=16716
Other problems can be swap, you might zero out all of swap, then have parts of
ram paged to disk again, leaving part of your disk unwiped.
So boot from whatever media you have, then wipe the disk.
So this isn't a bad idea:
$ dd if=/dev/urandom of=/dev/sda bs=1M
But keep in mind that unreliable sectors might still be readable and not
overwritten by the DD. The chances are small, but there.
On 2/3/24 12:36, Bob Scofield wrote:
Hi,
I want to recycle an old desktop. I'm planning to wipe the hard drive with
this command:
dd if=/dev/urandom of=/dev/sda bs=1M
Can I just run this from the command line? Or do I have to use a flash drive
with Linux on it and run it from the command line of the Linux on the flash drive?
Thanks.
Bob
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