MySQL (Percona 5.6) no se iniciará.

Este error me ha pasado varias veces. Cada vez, tuve que eliminar los directorios de datos de MySQL y reinstalar MySQL.

¿Hay otra forma de arreglar MySQL? (¿Específicamente uno en el que los datos no se borren?)

/var/log/mysql/error.log

150214 16:36:39 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
2015-02-14 16:36:40 0 [Warning] Using unique option prefix key_buffer instead of key_buffer_size is deprecated and will be removed in a future release. Please use the full name instead.
2015-02-14 16:36:40 0 [Warning] 'THREAD_CONCURRENCY' is deprecated and will be removed in a future release.
2015-02-14 16:36:40 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2015-02-14 16:36:40 1018 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead.
2015-02-14 16:36:40 1018 [Note] Plugin 'FEDERATED' is disabled.
/usr/sbin/mysqld: Incorrect file format 'plugin'
2015-02-14 16:36:40 1018 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2015-02-14 16:36:40 1018 [Note] InnoDB: Using atomics to ref count buffer pool pages
2015-02-14 16:36:40 1018 [Note] InnoDB: The InnoDB memory heap is disabled
2015-02-14 16:36:40 1018 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2015-02-14 16:36:40 1018 [Note] InnoDB: Memory barrier is not used
2015-02-14 16:36:40 1018 [Note] InnoDB: Compressed tables use zlib 1.2.8
2015-02-14 16:36:40 1018 [Note] InnoDB: Using Linux native AIO
2015-02-14 16:36:40 1018 [Note] InnoDB: Using CPU crc32 instructions
2015-02-14 16:36:40 1018 [Note] InnoDB: Initializing buffer pool, size = 256.0M
2015-02-14 16:36:40 1018 [Note] InnoDB: Completed initialization of buffer pool
2015-02-14 16:36:40 1018 [Note] InnoDB: Highest supported file format is Barracuda.
2015-02-14 16:36:40 1018 [Note] InnoDB: The log sequence numbers 714340126 and 714340126 in ibdata files do not match the log sequence number 716513090 in the ib_logfiles!
2015-02-14 16:36:40 1018 [Note] InnoDB: Database was not shutdown normally!
2015-02-14 16:36:40 1018 [Note] InnoDB: Starting crash recovery.
2015-02-14 16:36:40 1018 [Note] InnoDB: Reading tablespace information from the .ibd files...
2015-02-14 16:36:40 1018 [Note] InnoDB: Restoring possible half-written data pages 
2015-02-14 16:36:40 1018 [Note] InnoDB: from the doublewrite buffer...
InnoDB: Last MySQL binlog file position 0 292596, file name binlog.000056
2015-02-14 16:36:40 1018 [Note] InnoDB: 128 rollback segment(s) are active.
2015-02-14 16:36:40 1018 [Note] InnoDB: Waiting for purge to start
2015-02-14 16:36:40 1018 [Note] InnoDB:  Percona XtraDB (http://www.percona.com) 5.6.21-70.1 started; log sequence number 716513090
2015-02-14 16:36:40 1018 [Note] Recovering after a crash using binlog
2015-02-14 16:36:40 1018 [Note] Starting crash recovery...
2015-02-14 16:36:40 1018 [Note] Crash recovery finished.
2015-02-14 16:36:40 1018 [Note] RSA private key file not found: /var/lib/mysql//private_key.pem. Some authentication plugins will not work.
2015-02-14 16:36:40 1018 [Note] RSA public key file not found: /var/lib/mysql//public_key.pem. Some authentication plugins will not work.
2015-02-14 16:36:40 1018 [Note] Server hostname (bind-address): '*'; port: 3306
2015-02-14 16:36:40 1018 [Note] IPv6 is available.
2015-02-14 16:36:40 1018 [Note]   - '::' resolves to '::';
2015-02-14 16:36:40 1018 [Note] Server socket created on IP: '::'.
2015-02-14 16:36:40 1018 [ERROR] Fatal error: Can't open and lock privilege tables: Incorrect file format 'user'
150214 16:36:40 mysqld_safe mysqld from pid file /tmp/mysqld.pid ended