runtime: wrong Unix error code from panic.

[robpike]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version devel +baf3eb1625 Tue Mar 6 01:11:26 2018 +0000 darwin/amd64

% cat p.go
package main

func main() {
	panic(3)
}
% ./p
panic: 3

goroutine 1 [running]:
main.main()
	/Users/r/p.go:4 +0x39
% echo $?
2
% 

Exit code 2 traditionally means 'incorrect arguments', as in flag.Usage.

Panic should be something like 127 or 255 on Unix.

Reported by darren.e.grant@gmail.com on nuts.

[cachvico]

or simply 1 meaning 'general error' ?

(http://tldp.org/LDP/abs/html/exitcodes.html)

[robpike]

As has been pointed out in the mail thread, it might be best to leave this alone and say that the error that triggered this is in a program that takes exit code 2 as 'success'. That is certainly nonstandard.

[cachvico]

Sure, although a note in the language spec might avoid some similar confusion in the future..

I'll open an issue with Supervisor (http://supervisord.org/)

[andybons]

/cc @aclements

[ianlancetaylor]

E-mail thread is at https://groups.google.com/d/msg/golang-nuts/u9NgKibJsKI/XxCdDihFDAAJ .

[cachvico]

Thanks!

[odeke-em]

How's it going @cachvico? Any news from filing the bug with Supervisord?

@ianlancetaylor sure let's document in the spec that a panic returns a non-zero code to the shell.
@robpike @aclements shall we proceed with making a panic return 127 or 255? @robpike if you might have time, a reference to a UNIX manual would be useful for us to include in the commit for posterity.

[cachvico]

Thanks - note that the Supervisord issue should be fixed on their side as per the above linked issue.

[ianlancetaylor]

Exit status 127 is used by the shell to indicate "command not found."
Exit status 126 is used by the shell to indicate "command found but not executable."
Exit status values 128 and up are used by the shell to indicate exiting due to a signal.

If a C++ program exits due to an uncaught throw it raises SIGABRT and therefore exits with status 134 (on GNU/Linux).

If a Python program exits due to raising an exception, it exits with status 1.

I think we should change an unrecovered panic to exit with status 1 rather than 2. And we should document in the language spec that an uncaught panic will cause the program to exit with a non-zero exit status, but we shouldn't document it further.

[cachvico]

The quickest solution to the original problem would simply be a correction to the spec at https://golang.org/pkg/builtin/#panic

I've submitted a change at https://go-review.googlesource.com/c/go/+/167709 - is this correct?

[cachvico]

Beg pardon - just realised the previous post said not to document the value explicitly.

May I make the change suggested by @ianlancetaylor to change the process exit code 2 to 1, and correct my change to the comment appropriately?

This would involve an edit to src/runtime/signal_sighandler.go line 151, and a supporting test-case.

[odeke-em]

I've submitted a change at https://go-review.googlesource.com/c/go/+/167709 - is this correct?

Thanks for submitting the change @cachvico! I've posted some comments on it.

May I make the change suggested by @ianlancetaylor to change the process exit code 2 to 1, and correct my change to the comment appropriately?
This would involve an edit to src/runtime/signal_sighandler.go line 151, and a supporting test-case.

Oh yes you can, all yours but we can review and submit those changes piece-meal/independent of the docs update.

[cuonglm]

Exit status values 128 and up are used by the shell to indicate exiting due to a signal.

@ianlancetaylor Note that only values greater than 128 are used by the shell to indicate exiting due to a signal.

Some documents indicate that 128 is used to indicate an invalid argument to shell builtin exit, but POSIX leave that behavior unspecified.

[ianlancetaylor]

@Gnouc Thanks for the correction.

[cachvico]

Docs updated in f947c4d to reflect the behaviour of panic()

Thanks all!