prometheus/node_exporter · error

unable to list all threads for pid

Error message

unable to list all threads for pid: %d %w

What it means

After opening the task directory, getThreadStates calls fs.AllProcs() on it to list the pid's threads; a non-ignored error is wrapped as 'unable to list all threads for pid: %d'. Note the message omits a colon before %w. This aborts the thread-state accounting for the whole scrape.

Solutions

1. Read the wrapped cause: for EACCES/EPERM, grant the exporter user access (root, hidepid gid option, or LSM allow rule).
2. Verify the task directory is listable: ls /proc/<pid>/task as the exporter user.
3. If the process is exiting during scrape, upgrade node_exporter/procfs — newer code treats vanished entries as ignorable.
4. Retry the scrape; persistent failures indicate a systematic permission problem, not a race.

// check task dir listing works for the exporter user
if _, err := os.ReadDir("/proc/self/task"); err != nil {
    log.Printf("task listing broken: %v", err)
}

if err := c.Update(ch); err != nil {
    if strings.Contains(err.Error(), "unable to list all threads") {
        log.Printf("thread enumeration failed for a pid; check task dir permissions: %v", err)
        // retry on next scrape
    }
}

When it happens

Trigger: AllProcs() on the /proc/<pid>/task filesystem returns an error not classified as ignorable — readdir of the task directory failed with EACCES/EPERM or another non-ENOENT error.

Common situations: hidepid or LSM restrictions preventing task directory listing for other users' processes; procfs mount corruption; unusual container runtimes exposing a partial procfs.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• error reading task for pid
• error reading stat for pid
• unable to retrieve limit number of threads
• unable to list all processes
• error reading stat for pid

AI-assisted analysis of prometheus/node_exporter@17ddd77c59 (2026-09-07). Data as JSON: /api/errors/c42060662e8438ca. Report an issue: GitHub.

Appendix: source

Thrown at collector/processes_linux.go:165

func (c *processCollector) getThreadStates(pid int, pidStat procfs.ProcStat, threadStates map[string]int32) error {
	fs, err := procfs.NewFS(procFilePath(path.Join(strconv.Itoa(pid), "task")))
	if err != nil {
		if c.isIgnoredError(err) {
			c.logger.Debug("file not found when retrieving tasks for pid", "pid", pid, "err", err)
			return nil
		}
		c.logger.Debug("error reading tasks for pid", "pid", pid, "err", err)
		return fmt.Errorf("error reading task for pid %d: %w", pid, err)
	}

	t, err := fs.AllProcs()
	if err != nil {
		if c.isIgnoredError(err) {
			c.logger.Debug("file not found when retrieving tasks for pid", "pid", pid, "err", err)
			return nil
		}
		return fmt.Errorf("unable to list all threads for pid: %d %w", pid, err)
	}

	for _, thread := range t {
		if pid == thread.PID {
			threadStates[pidStat.State]++
			continue
		}
		threadStat, err := thread.Stat()
		if err != nil {
			if c.isIgnoredError(err) {
				c.logger.Debug("file not found when retrieving stats for thread", "pid", pid, "threadId", thread.PID, "err", err)
				continue
			}
			c.logger.Debug("error reading stat for thread", "pid", pid, "threadId", thread.PID, "err", err)
			return fmt.Errorf("error reading stat for pid:%d thread:%d err:%w", pid, thread.PID, err)
		}
		threadStates[threadStat.State]++
	}

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