Please describe the problem.

git annex sync does not report when git fetch and git push fail due to network issues. While git fetch's error messages are printed, the exit status of git annex sync will still be 0.

Looking at the source code, this seems to be a deliberate design decision. The synchronization operation are coded in such a way that failing to send/receive commits to/from a remote is not reported as an error. (See pullRemote and pushRemote in Command/Sync.hs.) This has the advantage of allowing the user to simply say git annex sync without worrying too much about whether all of their configured remotes are reachable.

However, this poses problems when trying to use git annex sync in an automated way. If networking issues (including authentication failures) are ignored, this can easily convince a script using git annex sync that the operation has succeeded, when in fact it has failed.

I can think of a few ways of addressing this issue:

1. Keep going of any of the pullRemote/pushRemote invocations fail, but keep track of the fact that something has failed, and exit with status 1 if this happens. This has the advantage that scripts will be properly alerted when things go wrong, but isn't strictly backwards compatible.
2. Add an option to git annex sync which causes any failures within pullRemote/pushRemote to be considered fatal errors. Perhaps the option could be called --batch or --report-errors. This would allow for strict backwards-compatibility.
3. Make failures of pullRemote/pushRemote fatal errors if exactly one remote is given on the command line. This isn't backwards compatible, and also has issues because the semantics are not necessarily obvious to those using git annex sync.

I'm sure there are other solutions, but I think users of git annex sync need a way of detecting network errors and responding to them appropriately. Especially when you're only trying to synchronize with a single remote, and failing to reach that remote is by definition a failure of the entire process.

What steps will reproduce the problem?

Attempt to pull from any standard properly-configured git-annex remote <REMOTE> with

 $ git annex sync <REMOTE>

when <REMOTE> is not reachable on the network. Then check the exit status with

 $ echo $?

You should get 0 as the result.

What version of git-annex are you using? On what operating system?

I'm using the latest version in Debian stable, 8.20210223-2.

Please provide any additional information below.

Not really sure what to put here. Except perhaps to apologize for the overly design-oriented bug report. Also, be aware that I'm more than happy to put in the legwork of fixing the issue I've described above. But I'd like to make sure we agree on a solution before I spend a lot of effort assembling a patch series.

Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Oh yes, I've used git annex for many years now to handle synchronizing files between various machines. Many thanks for your work on this project.