Troubleshoot "permission denied" from START SLAVE (1 reply)

When setting up a replication server, I can successfully connect to my main server using the `mysql` command-line tool:

mysql -u REMOTE_USER -P REMOTE_PORT -h REMOTE_HOST -p REMOTE_DATABASE

However, when I try to `START SLAVE`, the connection fails with the message `Can't connect to MySQL server on 'REMOTE_HOST' (13 "Permission denied")`.

Stranger still, the general log on the main server shows the cli `mysql`'s successful connection but doesn't show any attempts from the `START SLAVE` command. (If I intentionally use the wrong password with the cli `mysql`, though, the general log does show that failed attempt.) **How can I troubleshoot this?**

`SHOW SLAVE STATUS` outputs the following:

                Slave_IO_State: Connecting to master
                   Master_Host: REMOTE_HOST
                   Master_User: REMOTE_USER
                   Master_Port: REMOTE_PORT
                 Connect_Retry: 60
               Master_Log_File: mysql-bin.041115
           Read_Master_Log_Pos: 569520669
                Relay_Log_File: mysql-relay-bin.000001
                 Relay_Log_Pos: 4
         Relay_Master_Log_File: mysql-bin.041115
              Slave_IO_Running: Connecting
             Slave_SQL_Running: Yes
               Replicate_Do_DB: REMOTE_DATABASE
           Replicate_Ignore_DB: 
            Replicate_Do_Table: 
        Replicate_Ignore_Table: 
       Replicate_Wild_Do_Table: 
   Replicate_Wild_Ignore_Table: 
                    Last_Errno: 0
                    Last_Error: 
                  Skip_Counter: 0
           Exec_Master_Log_Pos: 569520669
               Relay_Log_Space: 256
               Until_Condition: None
                Until_Log_File: 
                 Until_Log_Pos: 0
            Master_SSL_Allowed: No
            Master_SSL_CA_File: 
            Master_SSL_CA_Path: 
               Master_SSL_Cert: 
             Master_SSL_Cipher: 
                Master_SSL_Key: 
         Seconds_Behind_Master: NULL
 Master_SSL_Verify_Server_Cert: No
                 Last_IO_Errno: 2003
                 Last_IO_Error: error connecting to master 'REMOTE_USER@REMOTE_HOST:REMOTE_PORT' - retry-time: 60  maximum-retries: 86400  message: Can't connect to MySQL server on 'REMOTE_HOST' (13 "Permission denied")
                Last_SQL_Errno: 0
                Last_SQL_Error: 
   Replicate_Ignore_Server_Ids: 
              Master_Server_Id: 0
                Master_SSL_Crl: 
            Master_SSL_Crlpath: 
                    Using_Gtid: No
                   Gtid_IO_Pos: 
       Replicate_Do_Domain_Ids: 
   Replicate_Ignore_Domain_Ids: 
                 Parallel_Mode: conservative
                     SQL_Delay: 259200
           SQL_Remaining_Delay: NULL
       Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
              Slave_DDL_Groups: 0
Slave_Non_Transactional_Groups: 0
    Slave_Transactional_Groups: 0