Are file shredding programs a placebo? Does it make a difference

>>56043154
1 pass is enough on any HDD made within the past 20 years. Doing it more times than that is for paranoia only.

Don't listen that "they can figure out what bit it was before the wipe if it's only 1 pass!" nonsense. It only works SLIGHTLY SLIGHTLY better than a 50/50 guess in the lab. The chances of them being able to recover 1-pass wipe bits to get any coherent information is astronomical, and for all intense and purposes, as good as a guess.

>>56043154 If you are wiping the encrypted volume header it might be worth it to overwrite it multiple times. It takes less then a second anyway.
Elsewise one pass with /dev/urandom to delete your data and one with /dev/zero to make disk to look like new is more than enough.
But keep in mind that data in remapped sectors will not be deleted.

Ssds is another story. They have huge (~5% of the capacity) reserved section which is used by the controller to move your data around and you do not have direct access to it. Sata secure erase feature is a joke.

If your filesystem is copy on write (btrfs, zfs), it is placebo unless you disable copy on write for that file beforehand (doable with btrfs at least).

If you care about your privacy, encrypt beforehand. If you want to wipe securely, wipe the entire drive; for a SSD, multiple passes may be necessary (without TRIM) to ensure it really is wiped.

>>56043154
1 is enough 99,9% of the time
but if you can afford it do 2-3x just in case

>>56044195
You can always shred the whole partition with dd.

Doesn't work as good on ssd.
cat /dev/null is faster than dd.
The only advantage of dd is that you can stop start anywhere, even the middle of a file.