juicedata/juicefs · warning

failed to parse listen port: %v

Error message

failed to parse listen port: %v

What it means

During `juicefs debug` pprof-port discovery, getPprofPort parses each `lsof -i -nP` LISTEN line for the target PID and extracts the port by splitting the second-to-last field on ':' and taking index 1. The parse runs inside an anonymous func with a deferred recover, so any panic (notably an index-out-of-range from splitting an address that contains no ':') is converted into this wrapped error. The wrapping exists precisely so one malformed lsof line cannot crash the whole debug command.

Source

Thrown at cmd/debug.go:195

	ret, err := exec.Command(lsofArgs[0], lsofArgs[1:]...).CombinedOutput()
	if err != nil {
		return 0, fmt.Errorf("failed to execute command `%s`: %v", strings.Join(lsofArgs, " "), err)
	}
	logger.Debugf("lsof output: \n%s", string(ret))
	lines := strings.Split(string(ret), "\n")
	if len(lines) == 0 {
		return 0, fmt.Errorf("pprof will be collected, but no listen port")
	}

	var listenPort = -1
	for _, line := range lines {
		fields := strings.Fields(line)
		if len(fields) != 0 {
			port, err := func() (port int, err error) {
				defer func() {
					e := recover()
					if e != nil {
						err = fmt.Errorf("failed to parse listen port: %v", e)
					}
				}()
				port, err = strconv.Atoi(strings.Split(fields[len(fields)-2], ":")[1])
				if err != nil {
					logger.Errorf("failed to parse port %v: %v", port, err)
				}
				return
			}()
			if err != nil {
				continue
			}
			if port >= 6060 && port <= 6099 && port > listenPort {
				if err := checkPort(port, amp); err == nil {
					listenPort = port
				}
				continue
			}
		}

View on GitHub (pinned to c9a67b23e8)

Solutions

1. Ignore safely: getPprofPort already `continue`s past lines that produce this error; verify other candidate ports in the 6060-6099 range are being tried.
2. Run `/bin/sh -c "lsof -i -nP | grep LISTEN | grep <pid>"` manually and inspect lines whose second-to-last field lacks a ':'; those are the offenders.
3. Ensure the JuiceFS mount exposes pprof (default net/http/pprof on 6060+) so a valid TCP line exists among lsof output.
4. Check lsof version/platform differences; prefer parsing the `*:PORT` / `127.0.0.1:PORT` address column explicitly rather than the second-to-last field.

Example fix

// before
port, err = strconv.Atoi(strings.Split(fields[len(fields)-2], ":")[1])
// after
addr := fields[len(fields)-2]
if i := strings.LastIndex(addr, ":"); i >= 0 {
    port, err = strconv.Atoi(addr[i+1:])
} else {
    err = fmt.Errorf("no port in address %q", addr)
}

addr := fields[len(fields)-2]
if i := strings.LastIndex(addr, ":"); i < 0 || i == len(addr)-1 {
    return fmt.Errorf("skipping line: no parsable port in address %q", addr)
}
port, err := strconv.Atoi(addr[i+1:])

func hasPort(addr string) bool {
    i := strings.LastIndex(addr, ":")
    return i >= 0 && i < len(addr)-1
}

// Go: recover converted to error (already used in getPprofPort)
defer func() {
    if e := recover(); e != nil {
        err = fmt.Errorf("failed to parse listen port: %v", e)
    }
}()

When it happens

Trigger: `juicefs debug <mountpoint>` runs lsof and a LISTEN line has fewer than 2 whitespace fields, or its second-to-last field is an address without ':' (e.g. a Unix socket line, an IPv6/pcrec-format line, or `fields[len(fields)-2]` being the PID itself), causing strings.Split(..., ":")[1] to panic. The recover converts the panic into 'failed to parse listen port: %v'.

Common situations: Environments whose lsof emits non-standard LISTEN lines (busybox lsof, unusual locales, IPv6 addresses, extra columns); the mount was started with a Unix-domain socket instead of a TCP listener; PID reuse picks up unrelated processes with non-TCP listening sockets.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• failed to execute command `%s`: %v
• error creating GET request: %v
• error GET request: %v
• error GET request, status code %d
• recovered from %s

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/8b7cfec3e9bf4694. Report an issue: GitHub.