magic(5) is a system for determining the type of a file by examining the 'magic bytes' at or near the start of a file.

For example, POSIX tar files have a defined file format that starts with a header struct: https://www.gnu.org/software/tar/manual/html_node/Standard.h...

You can see that at byte offset 257 is `char magic[6]`, which contains `TMAGIC`, which is the byte string "ustar\0". Thus, if a file has the bytes 'ustar\0' at offset 257 we can reasonably assume that it's a tar file. Almost every defined file type has some kind of string of 'magic' predefined bytes at a predefined location that lets a program know "yes, this is in fact a JPEG file" rather than just asserting "it says .jpg so let's try to interpret this bytestring and see what happens".

As for how it's similar: I don't think it actually is, I think that's a misunderstanding. The metadata that this vector FS is storing is more than "this is a a JPEG" or "this is a word document", as I understand it, so comparing it to magic(5) is extremely reductionist. I could be mistaken, however.

I think they're referring to this, https://linux.die.net/man/5/magic given the notation. That said I don't really see how it'd be all that relevant to the discussion so maybe i'm missing something else.

magic(5) means `man 5 magic`: https://linux.die.net/man/5/magic

It's just a tool that can read "magic bytes" to figure out what files contains. Very different from what VectorVFS is.

https://manpages.org/magic/5 is a database of file types, used by the file(1) command. I don't exactly follow how it's the same though; it would let you say "what files are videos" but not "what files are videos of a cat". Which is sort of related but unless I missed something there is a difference.

four people answered strictly correctly as to what magic(5) is, but not a single one realized that storing some aux data as xattr in linux FS is not in any way different from just storing the exact same data as a file header. which is how magic(5) works.

how come?

(besides good luck not forgetting to rsync those xattrs)