In POSIX, you can theoretically use inode zero

When I wrote about the length of file names in early Unix, I noted that inode numbers were unsigned 16-bit integers and thus you could only have at most 65,536 inodes in any given filesystem. Over on the Fediverse, JdeBP correctly noted that I had an off by one error. The original Unix directory entry format used a zero inode number to mark deleted entries, which meant that you couldn't actually use inode zero for anything (not even the root directory of the filesystem, which needed a non-zero inode number in order to have a '.' entry). (Contrary to what I said in that Fediverse thread, I think that V7 and earlier may not have actually had a zero inode. The magic happens in usr/sys/h/param.h in the itod() and itoo() macros. These give a result for inode 0, but I suspect they're never supposed to be used; if I'm doing it right, inode 1 is at offset 0 within block 2.) Since I'm the sort of person that I am, this made me wonder if you could legally use inode zero today in a POSIX compli ... Read full article.