The reason shred writes "multiple times with garbage" is due to magnetic disks where even when overwritten, old bit values could still be extracted with advanced tools. This is not the case for SSDs, so a single pass of shred (either random or zero) is enough here. Multiple passes will just kill your SSD faster.
The problem with sector access still stands, so you're not sure it's actually overwritten. You should use sfill(1) in addition to shred. sdmem(1) also, if you don't want to physically power down your machine.
>The reason shred writes "multiple times with garbage" is due to magnetic disks where even when overwritten, old bit values could still be extracted with advanced tools.
People thought that you needed multiple overwrites for traditional drives but in reality that data was gone after a single overwrite of 0. There were no "advanced techniques" that could recover the data. Some specs suggested multiple passes, but this was because they were using precautionary principle.
> This is not the case for SSDs, so a single pass of shred (either random or zero) is enough here. Multiple passes will just kill your SSD faster.
SSDs do weird things with the data, so if your data is important enough you should destroy the drives. There's some data tucked away in odd places.
Hum, no. Some time ago you needed multiple uncorrelated overwrites to hide your data. Then as HDDs shrank you strted needing less and less passes up to today that you just need to clear it once.
It's not about people thinking unrealistic things. The command was created for defending against a demonstrated attack.
> Some time ago you needed multiple uncorrelated overwrites to hide your data.
You really didn't. It's a really persistent myth that there's some secret technique to recover overwritten data. For PC hard drives "blobby bits" has never been a thing. It might have been a thing on 1970s style 24" disc platters, but we're not talking about those.
No one has ever recovered data from a drive that's had a single overwrite of zeros - no software claims to be able to do this, no recovery service claims to be able to do this, there are no published papers that claim to be able to do this (there's one that gets an accuracy of 50%-55% per bit, ie useless).
Since the early 1980s a single overwrite of 0 has been sufficient to destroy data.
And if you're worried about a well funded government agency that has the money to spend on exotic techniques you can do a single pass with random data, or NIST 7 passes, or you destroy the drive.
The problem with sector access still stands, so you're not sure it's actually overwritten. You should use sfill(1) in addition to shred. sdmem(1) also, if you don't want to physically power down your machine.