What causes "no matching process found" in pranshuparmar/witr?

Verify the process exists: run `ps aux | grep ` or `lsof -i : ` before invoking.

no matching process found

Error message

no matching process found

What it means

processTarget resolved the target (process name, pid, port, etc.) via target.Resolve and got no error but an empty pid list — the lookup succeeded syntactically yet matched nothing. The library converts the empty result into this explicit error and routes it through handleResolveError for reporting.

Source

Thrown at internal/app/app.go:417

	return string(data)
}

// processTarget handles resolving and rendering a single target.
// Returns the exit code for this target.
func processTarget(cmd *cobra.Command, outw io.Writer, outp output.Printer, t model.Target, flags appFlags, multiMode bool, jsonResults *[]string) int {
	colorEnabled := useColor(flags, outw)

	if flags.env {
		return processEnvTarget(outw, outp, t, flags, multiMode, jsonResults)
	}

	if t.Type == model.TargetContainer {
		return processContainerTarget(cmd, outw, outp, t, flags, multiMode, jsonResults)
	}

	pids, err := target.Resolve(t, flags.exact)
	if err == nil && len(pids) == 0 {
		err = fmt.Errorf("no matching process found")
	}
	if err != nil {
		return handleResolveError(cmd, outw, outp, t, err, flags, multiMode, jsonResults)
	}

	if len(pids) > 1 {
		if multiMode && flags.json {
			*jsonResults = append(*jsonResults, jsonErrorEntry(t, fmt.Sprintf("multiple processes matched (%d results)", len(pids))))
		} else {
			hint := "witr --pid <pid>"
			if flags.env {
				hint = "witr --pid <pid> --env"
			}
			printMultiMatch(outp, pids, colorEnabled, hint)
		}
		return ExitInvalidInput
	}

View on GitHub (pinned to dc4fa1da82)

Solutions

Verify the process exists: run `ps aux | grep <name>` or `lsof -i :<port>` before invoking.
Check the pid is current — the target may have exited; re-resolve it.
Drop --exact or use the full process name if exact matching filtered out your target.
Confirm user permissions: processes owned by other users may be hidden; retry with sudo.

Example fix

// before
cmd := exec.Command("errlookup", "myapp") // crashes: no match after restart
// after
if out, err := exec.Command("pgrep", "-x", "myapp").Output(); err != nil || len(out) == 0 {
    return fmt.Errorf("myapp is not running; start it before inspecting")
}
cmd := exec.Command("errlookup", "myapp")

Defensive patterns

Strategy: validation

Validate before calling

func processExists(name string) bool {
    out, err := exec.Command("pgrep", "-f", name).Output()
    return err == nil && len(strings.Fields(string(out))) > 0
}
if !processExists("myapp") {
    return errors.New("myapp is not running; nothing to inspect")
}

Try / catch

err := runLookup(target)
if err != nil && strings.Contains(err.Error(), "no matching process found") {
    log.Printf("target %q matched no process; skipping", target.Value)
    return nil
}
if err != nil { return err }

Prevention

Confirm the process/port exists with ps/lsof before lookup.
Re-resolve pids at run time instead of caching them across restarts.
Avoid --exact unless you pass the full, case-correct process name.
Run with sufficient privileges (same user or sudo) to see all processes.

When it happens

Trigger: A process-name target that matches no running process; a --pid whose process has exited; a --port with no listening socket; --exact matching where the name differs in case or suffix.

Common situations: Typos in process names; service already stopped/crashed; checking a port after the app moved to another port; using the exact flag with a truncated or case-mismatched name.

Related errors

AI-assisted analysis of pranshuparmar/witr@dc4fa1da82 (2026-09-01). Data as JSON: /api/errors/570493a7a51e457e. Report an issue: GitHub.