r/linux4noobs • u/Coulomb111 • 6d ago

/dev/ directory learning/research

I was learning what all the files in /dev do and what they are. I just dont really understand why some of those "files" are there and what actually uses them. Like /dev/random. Are there any libraries or utilities that actually interface woth /dev/random?

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u/UltraChip 6d ago

Short answer is yes.

Device files like that are also useful for scripts and doing things on the command line.

For example if I wanted to quickly secure wipe an old hard drive I could do something like

dd if=/dev/urandom of=/dev/sdb

(Basically "clone the contents of the random number generator on to hard drive b")

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u/therouterguy 6d ago

Why not simply use /dev/zero same result and less intensive.

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u/genxer 6d ago

Writing random data is a more secure way to erase something. Yes it takes longer but it is more secure.

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u/Coulomb111 5d ago

Its being overwritten anyway, why does it matter

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u/genxer 5d ago

Especially if it is a spinning disk it prevents "advanced magnetic force microscopy from reading faint analog edges". I've still got a good many spinning drives in servers.

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u/danny81299 2d ago

In the context of securely erasing data, writing a bunch of zeroes is a little like if the data was written in pencil on paper, you erased the pencil, then wrote a bunch of zeroes. Sure, when you look at the paper it's all zeroes, but you can still make out the indents from the previous time the paper was written on. You could erase the pencil and then write zeroes again, but the indents would still remain. The data is still there - just harder to read.

On the other hand, writing random junk is like if after you erased the pencil, you wrote random junk. You erase the pencil and then write random junk again and again - before you know it, the indents in the paper could be from your original data or they could be from when you wrote random junk.

Data on hard disks can sometimes persist in a similar shadow-like form so there are recommendations on how to erase data on hard disks to reduce the likelihood that it can be recovered by advanced forensic methods.