ubuntu 上 的mysql 启动不了了 [ 未指定版本 ]

sbw@~$mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

错误日志显示

150907 14:23:02 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
150907 14:23:02 [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.
150907 14:23:02 [Note] /usr/sbin/mysqld (mysqld 5.5.44-0ubuntu0.14.04.1) starting as process 11631 ...
150907 14:23:02 [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.
150907 14:23:02 [Note] Plugin 'FEDERATED' is disabled.
150907 14:23:02 [ERROR] Function 'innodb' already exists
150907 14:23:02 [Warning] Couldn't load plugin named 'innodb' with soname 'ha_innodb.so'.
150907 14:23:02 [ERROR] Function 'federated' already exists
150907 14:23:02 [Warning] Couldn't load plugin named 'federated' with soname 'ha_federated.so'.
150907 14:23:02 [ERROR] Function 'blackhole' already exists
150907 14:23:02 [Warning] Couldn't load plugin named 'blackhole' with soname 'ha_blackhole.so'.
150907 14:23:02 [ERROR] Function 'archive' already exists
150907 14:23:02 [Warning] Couldn't load plugin named 'archive' with soname 'ha_archive.so'.
150907 14:23:02 InnoDB: The InnoDB memory heap is disabled
150907 14:23:02 InnoDB: Mutexes and rw_locks use GCC atomic builtins
150907 14:23:02 InnoDB: Compressed tables use zlib 1.2.8
150907 14:23:02 InnoDB: Using Linux native AIO
150907 14:23:02 InnoDB: Initializing buffer pool, size = 128.0M
150907 14:23:02 InnoDB: Completed initialization of buffer pool
InnoDB: Error: log file ./ib_logfile0 is of different size 0 50331648 bytes
InnoDB: than specified in the .cnf file 0 5242880 bytes!
150907 14:23:02 [ERROR] Plugin 'InnoDB' init function returned error.
150907 14:23:02 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
150907 14:23:02 [ERROR] Unknown/unsupported storage engine: InnoDB
150907 14:23:02 [ERROR] Aborting

150907 14:23:02 [Note] /usr/sbin/mysqld: Shutdown complete

150907 14:23:02 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended