EC
1201
MySQLERRORNotableReplicationHIGH confidence

Could not initialize master info structure

Production Risk

High — replication cannot start until this is resolved.

What this means

ER_MASTER_INFO (1201, SQLSTATE HY000) is raised when MySQL cannot read or initialize the master info repository (master.info file or mysql.slave_master_info table). This prevents replication from starting.

Why it happens
  1. 1Corrupted master.info file or slave_master_info table
  2. 2Permission error on the data directory preventing master.info from being read
  3. 3Incompatible replication metadata after a failed upgrade
How to reproduce
trigger — this will error
trigger — this will error
START SLAVE;  -- fails if master info cannot be loaded

expected output

ERROR 1201 (HY000): Could not initialize master info structure; more error messages can be found in the MySQL error log

Fix

Reset and reconfigure slave

Reset and reconfigure slave
STOP SLAVE;
RESET SLAVE ALL;
CHANGE MASTER TO MASTER_HOST='host', MASTER_USER='repl', MASTER_PASSWORD='pw',
  MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=4;
START SLAVE;

Why this works

RESET SLAVE ALL clears the corrupted master info, allowing a clean reconfiguration.

Version notes

Sources
Official documentation ↗

MySQL 8.0 — 1201 ER_MASTER_INFO

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