nektos/act · error

bad mode specified: %s

Error message

bad mode specified: %s

What it means

In the three-segment case (host:container:mode), validateLinuxPath runs the third segment through the device-mode validator (a non-empty ordered subset of 'rwm'). If it is not a valid mode, 'bad mode specified' is returned showing the offending mode.

Source

Thrown at pkg/container/docker_cli.go:1129

	}
	switch len(split) {
	case 1:
		containerPath = split[0]
		val = path.Clean(containerPath)
	case 2:
		if isValid := validator(split[1]); isValid {
			containerPath = split[0]
			mode = split[1]
			val = fmt.Sprintf("%s:%s", path.Clean(containerPath), mode)
		} else {
			containerPath = split[1]
			val = fmt.Sprintf("%s:%s", split[0], path.Clean(containerPath))
		}
	case 3:
		containerPath = split[1]
		mode = split[2]
		if isValid := validator(split[2]); !isValid {
			return val, fmt.Errorf("bad mode specified: %s", mode)
		}
		val = fmt.Sprintf("%s:%s:%s", split[0], containerPath, mode)
	}

	if !path.IsAbs(containerPath) {
		return val, fmt.Errorf("%s is not an absolute path", containerPath)
	}
	return val, nil
}

// validateAttach validates that the specified string is a valid attach option.
func validateAttach(val string) (string, error) {
	s := strings.ToLower(val)
	if slices.Contains([]string{"stdin", "stdout", "stderr"}, s) {
		return s, nil
	}
	return val, errors.New("valid streams are STDIN, STDOUT and STDERR")
}

View on GitHub (pinned to 4f41128141)

Solutions

1. Use only the letters r, w, m for the mode, e.g. rwm, rw, or r
2. Drop the mode entirely for the default rwm: --device /dev/x:/dev/x
3. Do not use ro/rw/chmod octals — they are invalid for devices

Example fix

# before
--device /dev/x:/dev/x:ro

# after
--device /dev/x:/dev/x:r

// Go: mirror validDeviceMode
func isValidDeviceMode(m string) bool {
    if m == "" { return false }
    seen := map[rune]bool{}
    for _, r := range m {
        if r != 'r' && r != 'w' && r != 'm' { return false }
        if seen[r] { return false }
        seen[r] = true
    }
    return true
}

When it happens

Trigger: Passing a mode segment that is empty, contains letters outside r/w/m (e.g. 'rwxa'), or duplicates like 'rr'. Example: --device /dev/x:/dev/x:rox.

Common situations: Assuming chmod-style modes (4, 6, 755) or mount option vocabulary (ro, rw) instead of Docker's rwm device modes.

Related errors

• unknown server OS: %s
• invalid device specification: %s
• bad format for path: %s
• %s is not an absolute path
• --pid: invalid PID mode

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/0d610cab975019bb. Report an issue: GitHub.