go-delve/delve · error

errLogstrWithoutLog

errLogstrWithoutLog

Error message

--log-output specified without --log

What it means

pkg/logflags.Setup validates logging options: --log-output selects which log categories to emit, but it only takes effect when logging is enabled with --log. Passing a non-empty logstr with logFlag=false returns errLogstrWithoutLog because the output selector would be silently ignored.

Source

Thrown at pkg/logflags/logflags.go:189

		return
	}
	logger := rpcLogger(true)
	logger.Warnf("Listening for remote connections (connections are not authenticated nor encrypted)")
}

func WriteError(msg string) {
	if logOut != nil {
		fmt.Fprintln(logOut, msg)
	} else {
		fmt.Fprintln(os.Stderr, msg)
	}
}

func WriteCgoFlagsWarning() {
	makeLogger(true, "layer", "dlv").Warn("CGO_CFLAGS already set, Cgo code could be optimized.")
}

var errLogstrWithoutLog = errors.New("--log-output specified without --log")

// Setup sets debugger flags based on the contents of logstr.
// If logDest is not empty logs will be redirected to the file descriptor or
// file path specified by logDest.
func Setup(logFlag bool, logstr, logDest string) error {
	if logDest != "" {
		n, err := strconv.Atoi(logDest)
		if err == nil {
			logOut = os.NewFile(uintptr(n), "delve-logs")
		} else {
			fh, err := os.Create(logDest)
			if err != nil {
				return fmt.Errorf("could not create log file: %v", err)
			}
			logOut = fh
		}
	}
	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)

View on GitHub (pinned to a23773e6c3)

Solutions

1. Add the --log flag whenever --log-output is used
2. If you only need logs to a file/pipe, pass --log together with --log-output and --log-dest
3. Remove --log-output if verbose logging is not wanted

Example fix

// before
dlv debug --log-output=debugger main.go
// after
dlv debug --log --log-output=debugger main.go

if logOutput != "" && !logFlag {
    return fmt.Errorf("--log-output requires --log")
}
err := logflags.Setup(logFlag, logstr, logDest)

if err := logflags.Setup(logFlag, logstr, logDest); err != nil {
    if errors.Is(err, logflags.ErrLogstrWithoutLog) /* or message match */ {
        return fmt.Errorf("enable --log or drop --log-output: %w", err)
    }
    return err
}

When it happens

Trigger: Calling Setup(false, "debugger=1", "") or running dlv with --log-output=... but without --log.

Common situations: Command lines or launch configs that set log-output (copied from another invocation) while omitting --log; wrapper scripts that only partially forward logging flags.

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/667c459e7f1f5c93. Report an issue: GitHub.