# /etc/init.d/mysqld start
MySQL Daemon failed to start.
Starting mysqld:    [FAILED]

# tail -n 100 /var/log/mysqld.log
110813  5:30:26  InnoDB: Waiting for the background threads to start
110813  5:30:27 InnoDB: 1.1.8 started; log sequence number 351596238
110813  5:30:27 [ERROR] /usr/libexec/mysqld: unknown variable 'default-character-set=utf8'
110813  5:30:27 [ERROR] Aborting

unknown variable 'default-character-set=utf8' ってなんだ？

my.cnf の [client] セクションに default-character-set があるのが問題だと思います。
この行をコメントにするか、コマンドラインに --no-defaults オプションをつければ良いかと。

http://www.mysql.gr.jp/mysqlml/mysql/msg/12904

[mysqld]
#default-character-set = utf8

[mysql]
#default-character-set = utf8

[client]
#default-character-set = utf8

110813 05:33:59 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
110813  5:33:59 [Note] Plugin 'FEDERATED' is disabled.
/usr/libexec/mysqld: Table 'mysql.plugin' doesn't exist
110813  5:33:59 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
110813  5:33:59 InnoDB: The InnoDB memory heap is disabled
110813  5:33:59 InnoDB: Mutexes and rw_locks use InnoDB's own implementation
110813  5:33:59 InnoDB: Compressed tables use zlib 1.2.3
110813  5:33:59 InnoDB: Using Linux native AIO
110813  5:33:59 InnoDB: Initializing buffer pool, size = 128.0M
110813  5:33:59 InnoDB: Completed initialization of buffer pool
110813  5:33:59 InnoDB: highest supported file format is Barracuda.
110813  5:34:00  InnoDB: Waiting for the background threads to start
110813  5:34:01 InnoDB: 1.1.8 started; log sequence number 351596238
110813  5:34:01 [ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it
110813  5:34:01 [ERROR] Can't open and lock privilege tables: Table 'mysql.servers' doesn't exist
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_current' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'setup_consumers' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'setup_instruments' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'setup_timers' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'performance_timers' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'threads' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_thread_by_event_name' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_summary_by_instance' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'events_waits_summary_global_by_event_name' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'file_summary_by_event_name' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'file_summary_by_instance' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'mutex_instances' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'rwlock_instances' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'cond_instances' has the wrong structure
110813  5:34:01 [ERROR] Native table 'performance_schema'.'file_instances' has the wrong structure
110813  5:34:01 [ERROR] Column count of mysql.db is wrong. Expected 22, found 20. Created with MySQL 50077, now running 50515.
 Please use mysql_upgrade to fix this error.
110813  5:34:01 [ERROR] mysql.user has no `Event_priv` column at position 29
110813  5:34:01 [ERROR] Cannot open mysql.event
110813  5:34:01 [ERROR] Event Scheduler: An error occurred when initializing system tables. Disabling the Event Scheduler.
110813  5:34:01 [Note] /usr/libexec/mysqld: ready for connections.
Version: '5.5.15'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL) by Remi

# mysql_upgrade
mysqlcheck: Got error: 1045: Access denied for user 'root'@'localhost' (using password: NO) when trying to connect
FATAL ERROR: Upgrade failed

# mysql_upgrade -u root -p

Looking for 'mysql' as: mysql
Looking for 'mysqlcheck' as: mysqlcheck
Running 'mysqlcheck with default connection arguments
Running 'mysqlcheck with default connection arguments
dqn.mt_asset
error    : Table rebuild required. Please do "ALTER TABLE `mt_asset` FORCE" or dump/reload to fix it!
dqn.mt_asset_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_asset_meta` FORCE" or dump/reload to fix it!
dqn.mt_association                                 OK
dqn.mt_author
error    : Table rebuild required. Please do "ALTER TABLE `mt_author` FORCE" or dump/reload to fix it!
dqn.mt_author_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_author_meta` FORCE" or dump/reload to fix it!
dqn.mt_author_summary
error    : Table rebuild required. Please do "ALTER TABLE `mt_author_summary` FORCE" or dump/reload to fix it!
dqn.mt_blog
error    : Table rebuild required. Please do "ALTER TABLE `mt_blog` FORCE" or dump/reload to fix it!
dqn.mt_blog_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_blog_meta` FORCE" or dump/reload to fix it!
dqn.mt_category
error    : Table rebuild required. Please do "ALTER TABLE `mt_category` FORCE" or dump/reload to fix it!
dqn.mt_category_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_category_meta` FORCE" or dump/reload to fix it!
dqn.mt_comment
error    : Table rebuild required. Please do "ALTER TABLE `mt_comment` FORCE" or dump/reload to fix it!
dqn.mt_comment_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_comment_meta` FORCE" or dump/reload to fix it!
dqn.mt_config                                      OK
dqn.mt_entry
error    : Table rebuild required. Please do "ALTER TABLE `mt_entry` FORCE" or dump/reload to fix it!
dqn.mt_entry_meta
error    : Table rebuild required. Please do "ALTER TABLE `mt_entry_meta` FORCE" or dump/reload to fix it!
dqn.mt_entry_rev                                   OK
dqn.mt_entry_summary
error    : Table rebuild required. Please do "ALTER TABLE `mt_entry_summary` FORCE" or dump/reload to fix it!
dqn.mt_field
error    : Table rebuild required. Please do "ALTER TABLE `mt_field` FORCE" or dump/reload to fix it!
dqn.mt_fileinfo
error    : Table rebuild required. Please do "ALTER TABLE `mt_fileinfo` FORCE" or dump/reload to fix it!
dqn.mt_filter
error    : Table rebuild required. Please do "ALTER TABLE `mt_filter` FORCE" or dump/reload to fix it!
dqn.mt_ipbanlist
error    : Table rebuild required. Please do "ALTER TABLE `mt_ipbanlist` FORCE" or dump/reload to fix it!
dqn.mt_log
error    : Table rebuild required. Please do "ALTER TABLE `mt_log` FORCE" or dump/reload to fix it!
dqn.mt_notification
error    : Table rebuild required. Please do "ALTER TABLE `mt_notification` FORCE" or dump/reload to fix it!

[中略]

error    : Table upgrade required. Please do "REPAIR TABLE `help_topic`" or dump/reload to fix it!
mysql.host                                         OK
mysql.proc
error    : Table upgrade required. Please do "REPAIR TABLE `proc`" or dump/reload to fix it!
mysql.procs_priv                                   OK
mysql.tables_priv                                  OK
mysql.time_zone                                    OK
mysql.time_zone_leap_second                        OK
mysql.time_zone_name
error    : Table upgrade required. Please do "REPAIR TABLE `time_zone_name`" or dump/reload to fix it!
mysql.time_zone_transition                         OK
mysql.time_zone_transition_type                    OK
mysql.user                                         OK
others.hayaoki                                     OK
others.timestamp                                   OK

Repairing tables
dqntest.mt_asset                                   OK
dqntest.mt_asset_meta                              OK
dqntest.mt_author                                  OK
dqntest.mt_author_meta                             OK
dqntest.mt_author_summary                          OK
dqntest.mt_blog                                    OK
dqntest.mt_blog_meta                               OK
dqntest.mt_category                                OK
dqntest.mt_category_meta                           OK
dqntest.mt_comment                                 OK
dqntest.mt_comment_meta                            OK
dqntest.mt_entry                                   OK
dqntest.mt_entry_meta                              OK
dqntest.mt_entry_summary                           OK
dqntest.mt_field                                   OK
dqntest.mt_fileinfo                                OK
dqntest.mt_filter                                  OK
dqntest.mt_ipbanlist                               OK
dqntest.mt_log                                     OK
dqntest.mt_notification                            OK
dqntest.mt_objectasset                             OK
dqntest.mt_objectscore                             OK
dqntest.mt_objecttag                               OK
dqntest.mt_plugindata                              OK
dqntest.mt_role                                    OK
dqntest.mt_session                                 OK
dqntest.mt_tag                                     OK
dqntest.mt_tbping                                  OK
dqntest.mt_tbping_meta                             OK
dqntest.mt_template                                OK
dqntest.mt_template_meta                           OK
dqntest.mt_templatemap                             OK
dqntest.mt_touch                                   OK
dqntest.mt_ts_funcmap                              OK
dqntest.mt_ts_job                                  OK
dqntest.mt_visitorstats_view                       OK
mysql.help_category                                OK
mysql.help_keyword                                 OK
mysql.help_topic                                   OK
mysql.proc                                         OK
mysql.time_zone_name                               OK
Running 'mysql_fix_privilege_tables'...
OK

# /etc/init.d/mysqld restart
Stopping mysqld:                                           [  OK  ]
Starting mysqld:                                           [  OK  ]

# tail -n 100 /var/log/mysqld.log

110813  5:39:08 [Note] /usr/libexec/mysqld: Shutdown complete

110813 05:39:08 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
110813 05:39:10 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
110813  5:39:10 [Note] Plugin 'FEDERATED' is disabled.
110813  5:39:10 InnoDB: The InnoDB memory heap is disabled
110813  5:39:10 InnoDB: Mutexes and rw_locks use InnoDB's own implementation
110813  5:39:10 InnoDB: Compressed tables use zlib 1.2.3
110813  5:39:10 InnoDB: Using Linux native AIO
110813  5:39:10 InnoDB: Initializing buffer pool, size = 128.0M
110813  5:39:10 InnoDB: Completed initialization of buffer pool
110813  5:39:10 InnoDB: highest supported file format is Barracuda.
110813  5:39:10  InnoDB: Waiting for the background threads to start
110813  5:39:11 InnoDB: 1.1.8 started; log sequence number 356621572
110813  5:39:11 [Note] Event Scheduler: Loaded 0 events
110813  5:39:11 [Note] /usr/libexec/mysqld: ready for connections.
Version: '5.5.15'  socket: '/var/lib/mysql/mysql.sock'  port: 3306  MySQL Community Server (GPL) by Remi

参考