Git error "non-monotonic index"

Question

My `git` setup has a central repository to which I push. Today I decided to look at the central repository using `Git Extensions`, and it said that the repo has no commits (almost as if the repo was never created). Investigating this issue, I tried to clone the repo, and it gave me some weird errors I've never seen: ``` error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce0977348c53.idx error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce0977348c53.idx error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce0977348c53.idx error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce0977348c53.idx error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce0977348c53.idx error: non-monotonic index C:/Temp/N1/Netduino/.git/objects/pack/pack-29a18084cf61cd0322a6e9cfd485ce09…

Accepted Answer

(not a complete answer, but at least some clues, and a workaround)

That error message comes from the `sha1_file.c`, method `check_packed_git_idx()`,

```
nr = 0;
index = idx_map;
if (version > 1)
  index += 2; /* skip index header */
for (i = 0; i < 256; i++) {
  uint32_t n = ntohl(index[i]);
  if (n < nr) {
    munmap(idx_map, idx_size);
    return error("non-monotonic index %s", path);
  }
  nr = n;
}
```

with `ntohl` function being:

The ntohl function converts a `u_long` from TCP/IP network order to host byte order (which is little-endian on Intel processors).

The `ntohl` function returns the value supplied in the `netlong` parameter with the byte order reversed. If `netlong` is already in host byte order, then this function will reverse it. It is up to the application to determine if the byte order must be reversed.

The `ntohl` function takes a 32-bit number in TCP/IP network byte order (the `AF_INET` or `AF_INET6` address family) and returns a 32-bit number in host byte order.

It is called by:

- `open_pack_index()`, and

- `parse_pack_index()`

See the structure of a pack file in the SO question "Is the git binary diff algorithm (delta storage) standardized?":

The first one is also called by `builtin/fsck.c`, so you can try a git fsck --full --progress, in order to check if you have a local corruption of your pack files, or if it actually is a remote repo issue. Make sure you can replicate the issue on different OS and/or different version of Git.

The usual workaround, for a (here "Netduino") repo which seems to be forked around on GitHub, is to:

- clone another fork,

- restore one's own local modification from the corrupt repo, add them and commit them

- `push --force` back to one's own fork, in order to erase/reset the remote history by one with can be packed correctly

Git error "non-monotonic index"

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