This article mainly introduces errno related content. If I get new input, I will add the content one after another.

About errno

errno - number of last error

You can take a look at https://man7.org/linux/man-pages/man3/errno.3.html to know about what’s errno and how the errno is supported in POSIX and C99.

Man Page

       errno {name-or-code}

       errno [-ls] [--list]

       errno [-s] [--search] {word}

       errno [-S] [--search-all-locales] {word}

➜  git git:(tl/bitmap-append-trace2-outputs) ✗ errno -s direct 
ENOENT 2 No such file or directory
ENOTDIR 20 Not a directory
EISDIR 21 Is a directory
ENOTEMPTY 66 Directory not empty

20: ENOTDIR

In a recent Git patch, Junio C Hamano, the maintainer of the Git community, gave me the following advice about ENOTDIR:

One thing you should consider when writing a “this is an optional file and not finding it is perfectly fine” logic like this one is that you may or may not want to ignore ENOTDIR. ENOTDIR is what you get when you say open(“a/b”) and “a” exists as something other than a directory. If you have a path with a slash in bitmap_name, and if in a sane and healthy repository the leading path should always exist (i.e. the file “a/b” may be missing, but the directory “a/” should be there), then getting ENOTDIR is a noteworthy event. There may be cases where ENOTDIR can justifiably and should be ignored.

from https://public-inbox.org/git/xmqqpmibmjjs.fsf@gitster.g/