Documentation Home
MySQL Replication
Related Documentation Download this Excerpt
PDF (US Ltr) - 1.0Mb
PDF (A4) - 1.0Mb
HTML Download (TGZ) - 279.7Kb
HTML Download (Zip) - 294.5Kb

MySQL Replication  /  ...  /  Setting Up Replication with Existing Data

2.1.8 Setting Up Replication with Existing Data

When setting up replication with existing data, you will need to decide how best to get the data from the master to the slave before starting the replication service.

The basic process for setting up replication with existing data is as follows:

  1. With the MySQL master running, create a user to be used by the slave when connecting to the master during replication. See Section 2.1.3, “Creating a User for Replication”.

  2. If you have not already configured the server-id and enabled binary logging on the master server, you will need to shut it down to configure these options. See Section 2.1.1, “Setting the Replication Master Configuration”.

    If you have to shut down your master server, this is a good opportunity to take a snapshot of its databases. You should obtain the master status (see Section 2.1.4, “Obtaining the Replication Master Binary Log Coordinates”) before taking down the master, updating the configuration and taking a snapshot. For information on how to create a snapshot using raw data files, see Section 2.1.6, “Creating a Data Snapshot Using Raw Data Files”.

  3. If your master server is already correctly configured, obtain its status (see Section 2.1.4, “Obtaining the Replication Master Binary Log Coordinates”) and then use mysqldump to take a snapshot (see Section 2.1.5, “Creating a Data Snapshot Using mysqldump”) or take a raw snapshot of the live server using the guide in Section 2.1.6, “Creating a Data Snapshot Using Raw Data Files”.

  4. Update the configuration of the slave. See Section 2.1.2, “Setting the Replication Slave Configuration”.

  5. The next step depends on how you created the snapshot of data on the master.

    If you used mysqldump:

    1. Start the slave, using the --skip-slave-start option so that replication does not start.

    2. Import the dump file:

      shell> mysql < fulldb.dump

    If you created a snapshot using the raw data files:

    1. Extract the data files into your slave data directory. For example:

      shell> tar xvf dbdump.tar

      You may need to set permissions and ownership on the files so that the slave server can access and modify them.

    2. Start the slave, using the --skip-slave-start option so that replication does not start.

  6. Configure the slave with the replication coordinates from the master. This tells the slave the binary log file and position within the file where replication needs to start. Also, configure the slave with the login credentials and host name of the master. For more information on the CHANGE MASTER TO statement required, see Section 2.1.10, “Setting the Master Configuration on the Slave”.

  7. Start the slave threads:

    mysql> START SLAVE;

After you have performed this procedure, the slave should connect to the master and catch up on any updates that have occurred since the snapshot was taken.

If you have forgotten to set the server-id option for the master, slaves cannot connect to it.

If you have forgotten to set the server-id option for the slave, you get the following error in the slave's error log:

Warning: You should set server-id to a non-0 value if master_host
is set; we will force server id to 2, but this MySQL server will
not act as a slave.

You also find error messages in the slave's error log if it is not able to replicate for any other reason.

Once a slave is replicating, you can find in its data directory one file named and another named The slave uses these two files to keep track of how much of the master's binary log it has processed. Do not remove or edit these files unless you know exactly what you are doing and fully understand the implications. Even in that case, it is preferred that you use the CHANGE MASTER TO statement to change replication parameters. The slave will use the values specified in the statement to update the status files automatically.


The content of overrides some of the server options specified on the command line or in my.cnf. See Section 2.3, “Replication and Binary Logging Options and Variables”, for more details.

A single snapshot of the master suffices for multiple slaves. To set up additional slaves, use the same master snapshot and follow the slave portion of the procedure just described.

User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
  Posted by Brian Kinney on September 10, 2015
I had a slave lose sync, and was trying to restore everything, with a minimum of effort.
When you want to resync an existing slave that failed and won't resync, I highly recommend using the mysqldump --master-data method.

1) It grabs all files.
2) It will put them back where they belong for you.
3) It collects the master status, and embeds it as SQL code for use upon restore.
4) It does not require you to stop the existing service, as it does the lock and unlock tables for you.

Reminder: you have to START SLAVE; once your MySQL < dump.db is applied.
Please then wait a good 90 seconds before expecting a valid answer to the question SHOW SLAVE STATUS;
You are looking for a YES on Slave_IO_Running and Slave_SQL_Running fields.
Even if you are not immediately in sync, you probably will be soon.