vitessio/vitess · error

couldn't read my.cnf file: %v

Error message

couldn't read my.cnf file: %v

What it means

OpenMysqldAndMycnf reads the existing tablet's my.cnf from disk (ReadMycnf) to rebuild the Mycnf struct; a missing or unreadable/unparseable my.cnf produces this wrapped error. It is used by commands operating on an already-initialized MySQL instance.

Source

Thrown at go/vt/mysqlctl/cmd.go:61

	if err := mycnf.RandomizeMysqlServerID(); err != nil {
		return nil, nil, fmt.Errorf("couldn't generate random MySQL server_id: %v", err)
	}
	if mysqlSocket != "" {
		mycnf.SocketFile = mysqlSocket
	}

	dbconfigs.GlobalDBConfigs.InitWithSocket(mycnf.SocketFile, collationEnv)
	return NewMysqld(&dbconfigs.GlobalDBConfigs), mycnf, nil
}

// OpenMysqldAndMycnf returns a Mysqld and a Mycnf object to use for working with a MySQL
// installation that already exists. The Mycnf will be built based on the my.cnf file
// of the MySQL instance.
func OpenMysqldAndMycnf(tabletUID uint32, collationEnv *collations.Environment) (*Mysqld, *Mycnf, error) {
	// We pass a port of 0, this will be read and overwritten from the path on disk
	mycnf, err := ReadMycnf(NewMycnf(tabletUID, 0), 0)
	if err != nil {
		return nil, nil, fmt.Errorf("couldn't read my.cnf file: %v", err)
	}

	dbconfigs.GlobalDBConfigs.InitWithSocket(mycnf.SocketFile, collationEnv)
	return NewMysqld(&dbconfigs.GlobalDBConfigs), mycnf, nil
}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Verify the tablet UID and that `<vtdataroot>/vt_<uid>/my.cnf` exists.
2. Run `mysqlctl init` first if the instance was never initialized.
3. Restore the my.cnf file (from backup or re-run init-config) if deleted.
4. Check file permissions/readability for the mysqlctl user.

mycnfPath := filepath.Join(vtdataroot, fmt.Sprintf("vt_%d", tabletUID), "my.cnf")
if _, err := os.Stat(mycnfPath); os.IsNotExist(err) {
	return fmt.Errorf("run mysqlctl init first; %s missing", mycnfPath)
}

m, mycnf, err := mysqlctl.OpenMysqldAndMycnf(uid, collationEnv)
if err != nil && strings.Contains(err.Error(), "couldn't read my.cnf file") {
	// verify tablet UID or re-init the instance
}

When it happens

Trigger: Running mysqlctl commands (shutdown, start, reinit-config, teardown) for a tabletUID whose my.cnf does not exist, was deleted, or is corrupt.

Common situations: Wrong tablet UID passed on the command line, tablet never initialized (no prior `mysqlctl init`), my.cnf deleted by cleanup scripts, disk/permission problems.

Related errors

• couldn't generate random MySQL server_id: %v
• can't run init-db-sql-file (%v): %v
• no client certs for connection
• unexpected: query ended without no results and no error
• overflow

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/69396324ce808121. Report an issue: GitHub.