vitessio/vitess · error

could not read existing file %v: %v

Error message

could not read existing file %v: %v

What it means

Returned by mysqld config update logic when the existing (current) config file on disk cannot be read before applying updates, wrapping the I/O error.

Source

Thrown at go/vt/mysqlctl/mysqld.go:1581

		defer client.Close()
		return client.RefreshConfig(ctx)
	}

	log.Info("Checking for updates to my.cnf")
	f, err := os.CreateTemp(path.Dir(cnf.Path), "my.cnf")
	if err != nil {
		return fmt.Errorf("could not create temp file: %v", err)
	}

	defer os.Remove(f.Name())
	err = mysqld.initConfig(cnf, f.Name())
	if err != nil {
		return fmt.Errorf("could not initConfig in %v: %v", f.Name(), err)
	}

	existing, err := os.ReadFile(cnf.Path)
	if err != nil {
		return fmt.Errorf("could not read existing file %v: %v", cnf.Path, err)
	}
	updated, err := os.ReadFile(f.Name())
	if err != nil {
		return fmt.Errorf("could not read updated file %v: %v", f.Name(), err)
	}

	if bytes.Equal(existing, updated) {
		log.Info("No changes to my.cnf. Continuing.")
		return nil
	}

	backupPath := cnf.Path + ".previous"
	err = os.Rename(cnf.Path, backupPath)
	if err != nil {
		return fmt.Errorf("could not back up existing %v: %v", cnf.Path, err)
	}
	err = os.Rename(f.Name(), cnf.Path)
	if err != nil {

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Verify cnf.Path exists and is readable by the current user.
2. If my.cnf was intentionally removed, reinitialize the tablet config instead of refreshing.
3. Fix permissions: chown/chmod the my.cnf file.
4. Point cnf.Path at the correct config location for this tablet.

Example fix

// before
rm /vt/vtdataroot/vt_0000000100/my.cnf  # then RefreshConfig fails
// after
vttablet reinit (or restore my.cnf from my.cnf.previous) before refreshing

if _, err := os.Stat(cnf.Path); err != nil {
    return fmt.Errorf("existing my.cnf %s missing; reinit required before refresh", cnf.Path)
}

if err := mysqld.RefreshConfig(ctx, cnf); err != nil {
    if strings.Contains(err.Error(), "could not read existing file") {
        log.Errorf("my.cnf absent/unreadable at %s; reinitialize config", cnf.Path)
    }
    return err
}

When it happens

Trigger: Mysqld.RefreshConfig after successfully writing the temp config: os.ReadFile(cnf.Path) fails because my.cnf was deleted, moved, or has bad permissions.

Common situations: First-time refresh before my.cnf ever written in an unexpected code path; manual cleanup removed my.cnf; tablet directory partially deleted; user running refresh differs from owner of my.cnf.

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

• could not create temp file: %v
• cannot stat hook %v: %v
• unable to create file: %v
• could not back up existing %v: %v
• failure creating directory %s: %w

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/b9ca5f0231df91fe. Report an issue: GitHub.