Linux libc4 knows about the five C standard flags. It knows about the length modifiers h, l, L, and the conversions c, d, e, E, f, F, g, G, i, n, o, p, s, u, x, and X, where F is a synonym for f. Additionally, it accepts D, O, and U as synonyms for ld, lo, and lu. (This is bad, and caused serious bugs later, when support for %D disappeared.)