cloudflare/cloudflared · error

error retrieving output from command '%s': %w

Error message

error retrieving output from command '%s': %w

What it means

collectDiskVolumeInformationUnix runs 'df -k' via exec.CommandContext and this error wraps any failure of command.Output() — meaning df could not be executed or exited non-zero. The command's string form and the underlying exec error are wrapped so you can see both which command failed and why (not-found, exit status, signal). It is raised before any parsing happens, so it always indicates an execution/environment problem, not a data-format problem.

Source

Thrown at diagnostic/system_collector_utils.go:344

	builder.WriteString("---END Memory information\n")
	builder.WriteString("---BEGIN File descriptors information\n")
	formatInfo(fdInfoRaw, &builder)
	builder.WriteString("---END File descriptors information\n")
	builder.WriteString("---BEGIN Disks information\n")
	formatInfo(disksRaw, &builder)
	builder.WriteString("---END Disks information\n")

	rawInformation := builder.String()

	return rawInformation
}

func collectDiskVolumeInformationUnix(ctx context.Context) ([]*DiskVolumeInformation, string, error) {
	command := exec.CommandContext(ctx, "df", "-k")

	stdout, err := command.Output()
	if err != nil {
		return nil, "", fmt.Errorf("error retrieving output from command '%s': %w", command.String(), err)
	}

	output := string(stdout)

	disks, err := ParseDiskVolumeInformationOutput(output, 1, 1)
	if err != nil {
		return nil, output, err
	}

	// returning raw output in case other collected information
	// resulted in errors
	return disks, output, nil
}

func collectOSInformationUnix(ctx context.Context) (*OsInfo, string, error) {
	command := exec.CommandContext(ctx, "uname", "-a")

	stdout, err := command.Output()

View on GitHub (pinned to 2253eeeb25)

Solutions

  1. Check the wrapped error: 'exec: "df": executable file not found in $PATH' means install/restore df (e.g. apt-get install coreutils / use a fuller base image).
  2. Run 'df -k' manually as the same user to see the non-zero exit reason; fix the offending mount (e.g. unmount stale NFS entries with 'umount -l').
  3. Verify PATH includes /bin and /usr/bin for the process user (containers and systemd units often have trimmed PATH).
  4. If the error is 'context deadline exceeded' or 'signal: killed', increase the diagnostic timeout or resolve the slow mount causing df to hang.
  5. Confirm no MAC policy (SELinux/AppArmor) blocks executing df for the cloudflared process.

Example fix

// before: distroless container image
FROM gcr.io/distroless/static

// after: image that includes df
FROM alpine:3.19
RUN apk add --no-cache coreutils
Defensive patterns

Strategy: try-catch

Validate before calling

if _, err := exec.LookPath("df"); err != nil {
    return fmt.Errorf("df not available in PATH: %w", err)
}

Type guard

func canRunDF() bool {
    return exec.Command("df", "-k").Run() == nil || func() bool {
        _, err := exec.LookPath("df")
        return err == nil
    }()
}

Try / catch

disks, raw, err := collector.Collect(ctx)
if err != nil && strings.Contains(err.Error(), "error retrieving output from command 'df") {
    log.Warn().Err(err).Msg("disk volume collection failed; check df availability and mounts")
    // proceed without disk info or retry with a longer deadline
}

Prevention

When it happens

Trigger: Collect() invokes collectDiskVolumeInformationUnix on a Unix system; 'df' is not in PATH, is not executable, the context is cancelled before completion, or df exits non-zero (e.g. a stale NFS mount hang or permission problem on a mounted filesystem).

Common situations: Minimal Docker images without coreutils' df (distroless/scratch images), restricted PATH in systemd services or containers, hung network mounts making df block until the request context times out, or SELinux/AppArmor policies denying exec.

Related errors

AI-assisted analysis of cloudflare/cloudflared@2253eeeb25 (2026-09-06). Data as JSON: /api/errors/a07165467a9753d5. Report an issue: GitHub.