I’m relatively new to signing my commits. And I recently stumbled into a new somewhat cryptic Git error. Here’s what I did to debug the problem. Hope it helps you.
The scenario: You have Git configured to use a GPG signing key for your commits. You craft a solid commit message, hit enter, and…
> git commit -m -S "my awesome commit"
error: gpg failed to sign the data
fatal: failed to write commit object
So Git was not able to write our commit due to some issue with GPG. Since we don’t know what the actual problem is or what a potential fix could be we need to dive deeper.
Peeking under the hood with Git Tracing:
To understand the execution of internal commands we can enable tracing. This helps us pinpoint the exact point of failure. To enable it, run:
GIT_TRACE=1 git commit -m -S "my awesome commit"
You get some output similar to:
23:38:32.290382 exec-cmd.c:139 trace: resolved executable path from Darwin stack: /Library/Developer/CommandLineTools/usr/bin/git
23:38:32.290775 exec-cmd.c:238 trace: resolved executable dir: /Library/Developer/CommandLineTools/usr/bin
23:38:32.291292 git.c:460 trace: built-in: git commit -m -S 'my awesome commit'
23:38:32.294327 run-command.c:655 trace: run_command: gpg --status-fd=2 -bsau 984DD2C2F09F6B95
error: gpg failed to sign the data
fatal: failed to write commit object
Identifying the Culprit:
In my case, I can see the last command to execute before failing was:
gpg --status-fd=2 -bsau 984DD2C2F09F6B95
Now, if I execute this command I might get more info on the actual problem.
[GNUPG:] KEYEXPIRED 1721848046
[GNUPG:] KEY_CONSIDERED 70F192BB37619BDBD39E43E4884DF2C2E09F6B95 3
gpg: skipped "884DF2C2E09F6B95": Unusable secret key
[GNUPG:] INV_SGNR 9 884DF2C2E09F6B95
[GNUPG:] FAILURE sign 54
gpg: signing failed: Unusable secret key
Ah-ha! The Expired Key:
So in my case, the problem is simple: an expired GPG Key. We just need to create a new GPG Key, sign it, then upload it to Github.
Bonus Tip: