slackhq/nebula · error

error while reading ca: %w

Error message

error while reading ca: %w

What it means

verify opens the CA bundle via openInput('ca', caPath) before building the trust pool. If opening/reading the CA input fails (file missing, unreadable, stdin claim conflict), the error is wrapped with this message and verification cannot proceed.

Source

Thrown at cmd/nebula-cert/verify.go:52

	if err := mustFlagString("ca", vf.caPath); err != nil {
		return err
	}
	if err := mustFlagString("crt", vf.certPath); err != nil {
		return err
	}

	var claims ioClaims
	if err := reserveInputs(&claims,
		"ca", *vf.caPath,
		"crt", *vf.certPath,
	); err != nil {
		return err
	}

	caReader, err := openInput("ca", *vf.caPath, &claims)
	if err != nil {
		return fmt.Errorf("error while reading ca: %w", err)
	}
	defer caReader.Close()

	caPool, err := cert.NewCAPoolFromPEMReader(caReader)
	if err != nil && !errors.Is(err, cert.ErrExpired) {
		return fmt.Errorf("error while adding ca cert to pool: %w", err)
	}

	rawCert, err := readInput("crt", *vf.certPath, &claims)
	if err != nil {
		return fmt.Errorf("unable to read crt: %w", err)
	}
	var errs []error
	for {
		if len(rawCert) == 0 {
			break
		}
		c, extra, err := cert.UnmarshalCertificateFromPEM(rawCert)

View on GitHub (pinned to dd8f660c0a)

Solutions

1. Verify the -ca path points to an existing, readable PEM file (cat it to confirm)
2. Run the command from the directory containing the CA or use an absolute path
3. Fix permissions (chmod/chown) on the CA file
4. If using '-' for stdin, ensure no other input flag also uses '-'

Example fix

// before
./nebula-cert verify -ca ca.crt -crt host.crt   # ca.crt not in cwd
// after
./nebula-cert verify -ca /etc/nebula/ca.crt -crt host.crt

import "os"
func checkReadable(path string) error {
    if path == "-" { return nil }
    fi, err := os.Stat(path)
    if err != nil { return err }
    if fi.IsDir() { return fmt.Errorf("%s is a directory", path) }
    f, err := os.Open(path)
    if err != nil { return err }
    return f.Close()
}
// err := checkReadable(caPath) before invoking verify

out, err := exec.Command("nebula-cert", "verify", args...).CombinedOutput()
if err != nil && strings.Contains(string(out), "error while reading ca") {
    log.Printf("CA unreadable: %s", out)
}

When it happens

Trigger: openInput returns an error for the -ca flag: -ca file does not exist, lacks read permission, is a directory, or two input flags both claim stdin.

Common situations: Wrong path to the CA PEM; running from a different working directory than assumed; missing read permissions; passing '-' to -ca while another input also uses '-'.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

• error while adding ca cert to pool: %w
• unable to read crt: %w
• error while writing out-key: %s
• error while writing out-crt: %s
• error while generating qr code: %s

AI-assisted analysis of slackhq/nebula@dd8f660c0a (2026-09-03). Data as JSON: /api/errors/c81ee75bc2c065b9. Report an issue: GitHub.