MySQL simple replication problem: 'show master status' produces 'Empty set'?

Question

I've been setting up MySQL master replication (on Debian 6.0.1) following these instructions faithfully: http://www.neocodesoftware.com/replication/

I've got as far as:

mysql > show master status;

but this is unfortunately producing the following, rather than any useful output:

Empty set (0.00 sec)

The error log at /var/log/mysql.err is just an empty file, so that's not giving me any clues.

Any ideas?

This is what I have put in /etc/mysql/my.cnf on one server (amended appropriately for the other server):

server-id = 1
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 1
master-host = 10.0.0.3
master-user = <myusername>
master-password = <mypass>
master-connect-retry = 60
replicate-do-db = fruit
log-bin = /var/log/mysql-replication.log
binlog-do-db = fruit

And I have set up users and can connect from MySQL on Server A to the database on Server B using the username/password/ipaddress above.

Solution 1

Interestingly, I have mysql running on my PC with binary logs not enabled. I did the following:

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 19
Server version: 5.5.12 MySQL Community Server (GPL)

Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show master status;
Empty set (0.00 sec)

mysql> show binary logs;
ERROR 1381 (HY000): You are not using binary logging

mysql>

As shown, since MySQL shows "Empty Set" for SHOW MASTER STATUS; because binary logging was not enabled. That's obvious given the configuration I have.

First thing you should do is make sure the error log has a specific folder

[mysqld]
log-error=/var/log/mysql/mysql.err
log-bin = /var/log/mysql/mysql-replication.log

Then run the following:

service mysql stop
mkdir /var/log/mysql
chown -R mysql:mysql /var/log/mysql
service mysql start

Then in the mysql client run these SQL Commands

SHOW MASTER STATUS;
SHOW BINARY LOGS;

If you get the same output I had before, then MySQL cannot write binary logs to the designated folder. Your dilemma becomes why MySQL cannot write to /var/log.

This is not a full answer but I hope this helps.

Solution 2

If thhe Mysql version is >5.0, your replication settings master-host, master-user, master-password and a few others in your my.cnf will be ignored. Use CHANGE MASTER TO for initial replication setup.

Compare http://dev.mysql.com/doc/refman/5.1/en/replication-howto-slaveinit.html

Comments

[Admin]

I've also tried following the simpler instructions at: howtoforge.com/mysql_database_replication (on one server alone) and again, when I get to show master status I see Empty set. Baffled!

[Admin]

Restart the service & check. If any error logs generated after restart, paste that also.

[John Hunt]

Setting /var/log to be recursively owned and with a group of mysql is going to break a linux system fairly badly. I strongly advise people not to do this. Instead, run that specifically on the log file which mysql is trying to write to, and if it's not there touch it first.

[RolandoMySQLDBA]

You know something, @JohnHunt ? You are right. I will change the folder.

[Stephan Vierkant]

--log-bin=file_name (dev.mysql.com/doc/refman/5.7/en/…). What manual states that it isn't a filename?