As reported by Nadav Har'El in https://bugzilla.kernel.org/show_bug.cgi?id=197961 The write(2) manual page has this paragraph: "On success, the number of bytes written is returned (zero indicates nothing was written). It is not an error if this number is smaller than the number of bytes requested; this may happen for example because the disk device was filled. See also NOTES." I find a few problems with this paragraph: 1. It's not clear what "See also NOTES." refers to (does it refer to anything?). What in the NOTES is relevant here? 2. The paragraph seems to suggest that write(2) of a non-empty buffer may sometimes return even 0 in case of an error like the device being filled. I think this is wrong - if there was an error after already writing some number of bytes, this non-zero number is returned. But if there's an error before writing any bytes, -1 will be returned (and the error reason in errno) - 0 will not be returned unless the given count is 0 (that case is explained in the following paragraph). 3. The paragraph doesn't explain what a user should do after a short write (i.e., write(2) returning less than count). How would the user know why there was an error, or if there even was one? I think users should be told what to do next because this information is part of how to use this API correctly. I think users should be told to retry the rest of the write (i.e., write(fd, buf+ret, count-ret) and this will either succeed in writing some more data if the error reason was solved, or the second write will return -1 and the error reason in errno. Reported-by: Nadav Har'El <nyh@math.technion.ac.il> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>