Our replication recently stopped working. I submitted a question but was unsuccessful in fixing the problem (Error 1236 - "Could not find first log file name in binary log index file"). Since the occurrence of the events described in the question, I've executed a RESET MASTER on the master, a RESET SLAVE on the slave, and created a new full dump, but am still getting the same results.

I thought I'd take a step back and try taking a different approach, attacking the specifics of the error message itself.

When I execute SHOW SLAVE STATUS on the slave, it reports that the master cannot "find first log file name":

Got fatal error 1236 from master when reading data from binary log: 'Could not find first log file name in binary log index file'

The "first log file name" is /var/lib/mysql/mysql-bin.000001:

root@master [905 13:30:56 /var/lib/mysql]# cat mysql-bin.index
/var/lib/mysql/mysql-bin.000001
/var/lib/mysql/mysql-bin.000002
/var/lib/mysql/mysql-bin.000003
/var/lib/mysql/mysql-bin.000004
/var/lib/mysql/mysql-bin.000005
/var/lib/mysql/mysql-bin.000006

MySQL itself seems to be aware that mysql-bin.000001 is the first binary log:

MariaDB [(none)]> SHOW BINARY LOGS;
+------------------+------------+
| Log_name         | File_size  |
+------------------+------------+
| mysql-bin.000001 |      10421 |
| mysql-bin.000002 | 1073919628 |
| mysql-bin.000003 | 1074488806 |
| mysql-bin.000004 | 1073744707 |
| mysql-bin.000005 | 1074366770 |
| mysql-bin.000006 | 1069984818 |
+------------------+------------+
6 rows in set (0.00 sec)

mysqlbinlog shows that this file seems to be accessible and valid:

root@master [911 13:48:04 /var/lib/mysql]# mysqlbinlog /var/lib/mysql/mysql-bin.000001
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;
/*!40019 SET @@session.max_insert_delayed_threads=0*/;
/*!50003 SET @OLD_COMPLETION_TYPE=@@COMPLETION_TYPE,COMPLETION_TYPE=0*/;
DELIMITER /*!*/;
# at 4
#160526 12:24:14 server id 5  end_log_pos 248   Start: binlog v 4, server v 10.0.21-MariaDB-log created 160526 12:24:14 at startup

MySQL itself also seems to have access to this first log file:

MariaDB [(none)]> SHOW BINLOG EVENTS in 'mysql-bin.000001' from 0 limit 4;
+------------------+-----+-------------------+-----------+-------------+------------------------------------------------+
| Log_name         | Pos | Event_type        | Server_id | End_log_pos | Info                                           |
+------------------+-----+-------------------+-----------+-------------+------------------------------------------------+
| mysql-bin.000001 |   4 | Format_desc       |         5 |         248 | Server ver: 10.0.21-MariaDB-log, Binlog ver: 4 |
| mysql-bin.000001 | 248 | Gtid_list         |         5 |         273 | []                                             |
| mysql-bin.000001 | 273 | Binlog_checkpoint |         5 |         312 | mysql-bin.000001                               |
| mysql-bin.000001 | 312 | Gtid              |         5 |         350 | BEGIN GTID 0-5-1                               |
+------------------+-----+-------------------+-----------+-------------+------------------------------------------------+
4 rows in set (0.00 sec)

Question

To recap, MySQL is complaining that it "Could not find first log file name in binary log index file". However, as shown above, it appears that MySQL does know what the "first log file name" is, and it can, indeed, access it.

What else should I check to ensure that MySQL can actually "find [the] first log file name"?