错误日志
在mysql数据库中，错误日志功能是默认开启的。并且，错误日志无法被禁止。默认情况下，错误日志存储在mysql数据库的数据文件中。错误日志文件通常的名称为hostname.err。其中，hostname表示服务器主机名。
错误日志信息可以自己进行配置的，错误日志所记录的信息是可以通过log-error和log-warnings来定义的，其中log-err是定义是否启用错误日志的功能和错误日志的存储位置，log-warnings是定义是否将警告信息也定义至错误日志中。默认情况下错误日志大概记录以下几个方面的信息：服务器启动和关闭过程中的信息（未必是错误信息，如mysql如何启动InnoDB的表空间文件的、如何初始化自己的存储引擎的等等）、服务器运行过程中的错误信息、事件调度器运行一个事件时产生的信息、在从服务器上启动服务器进程时产生的信息。mysql> SHOW GLOBAL VARIABLES LIKE '%log%';
+-----------------------------------------+---------------------------------------+
| Variable_name | Value |
+-----------------------------------------+---------------------------------------+
| back_log | 80 |
| binlog_cache_size | 32768 |
| binlog_checksum | CRC32 |
| binlog_direct_non_transactional_updates | OFF |
| binlog_error_action | IGNORE_ERROR |
| binlog_format | STATEMENT |
| binlog_gtid_simple_recovery | OFF |
| binlog_max_flush_queue_time | 0 |
| binlog_order_commits | ON |
| binlog_row_image | FULL |
| binlog_rows_query_log_events | OFF |
| binlog_stmt_cache_size | 32768 |
| binlogging_impossible_mode | IGNORE_ERROR |
| expire_logs_days | 0 |
| general_log | OFF |
| general_log_file | /mysql/data/localhost.log |
| innodb_api_enable_binlog | OFF |
| innodb_flush_log_at_timeout | 1 |
| innodb_flush_log_at_trx_commit | 1 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_buffer_size | 8388608 |
| innodb_log_compressed_pages | ON |
| innodb_log_file_size | 50331648 |
| innodb_log_files_in_group | 2 |
| innodb_log_group_home_dir | ./ |
| innodb_mirrored_log_groups | 1 |
| innodb_online_alter_log_max_size | 134217728 |
| innodb_undo_logs | 128 |
| log_bin | OFF |
| log_bin_basename | |
| log_bin_index | |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
| log_error | /mysql/data/localhost.localdomain.err |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| log_throttle_queries_not_using_indexes | 0 |
| log_warnings | 1 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_size | 1073741824 |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_relay_log_size | 0 |
| relay_log | |
| relay_log_basename | |
| relay_log_index | |
| relay_log_info_file | relay-log.info |
| relay_log_info_repository | FILE |
| relay_log_purge | ON |
| relay_log_recovery | OFF |
| relay_log_space_limit | 0 |
| simplified_binlog_gtid_recovery | OFF |
| slow_query_log | OFF |
| slow_query_log_file | /mysql/data/localhost-slow.log |
| sql_log_bin | ON |
| sql_log_off | OFF |
| sync_binlog | 0 |
| sync_relay_log | 10000 |
| sync_relay_log_info | 10000 |
+-----------------------------------------+---------------------------------------+
61 rows in set (0.00 sec)
log_error可以直接定义为文件路径，也可以为ON|OFF；log_warings只能使用1|0来定义开关启动。
更改错误日志位置可以使用log_error来设置形式如下：
默认的错误日志存放在data目录下，下面我们修改存放路径到/mysql/log下
[client]
#password = your_password
port = 3306
socket = /tmp/mysql.sock
[mysqld]
port = 3306
socket = /tmp/mysql3306.sock
datadir = /mysql/data
server-id = 1
log-error = /mysql/log/mysql.log
log-warings = 1 -----这里刻意写错
[root@localhost mysql]# mysqladmin -uroot -proot123 shutdown
Warning: Using a password on the command line interface can be insecure.
150615 09:48:53 mysqld_safe mysqld from pid file /mysql/data/localhost.localdomain.pid ended
[1]+ Done mysqld_safe --defaults-file=/mysql/my.cnf --user=mysql
[root@localhost mysql]# mysqld_safe --defaults-file=/mysql/my.cnf --user=mysql &
[1] 3133
[root@localhost mysql]# 150615 09:49:18 mysqld_safe Logging to '/mysql/log/mysql.log'.
150615 09:49:18 mysqld_safe Starting mysqld daemon with databases from /mysql/data
150615 09:49:20 mysqld_safe mysqld from pid file /mysql/data/localhost.localdomain.pid ended
[1]+ Done mysqld_safe --defaults-file=/mysql/my.cnf --user=mysql
启动后查看错误日志
[root@localhost log]# more mysql.log
150615 09:49:18 mysqld_safe Starting mysqld daemon with databases from /mysql/data
2015-06-15 09:49:18 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server
option (see documentation for more details).
2015-06-15 09:49:18 0 [Note] /mysql/bin/mysqld (mysqld 5.6.25-enterprise-commercial-advanced) starting as process 3289 ...
2015-06-15 09:49:18 3289 [Note] Plugin 'FEDERATED' is disabled.
2015-06-15 09:49:18 3289 [Note] InnoDB: Using atomics to ref count buffer pool pages
2015-06-15 09:49:18 3289 [Note] InnoDB: The InnoDB memory heap is disabled
2015-06-15 09:49:18 3289 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2015-06-15 09:49:18 3289 [Note] InnoDB: Memory barrier is not used
2015-06-15 09:49:18 3289 [Note] InnoDB: Compressed tables use zlib 1.2.3
2015-06-15 09:49:18 3289 [Note] InnoDB: Using Linux native AIO
2015-06-15 09:49:18 3289 [Note] InnoDB: Using CPU crc32 instructions
2015-06-15 09:49:18 3289 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2015-06-15 09:49:18 3289 [Note] InnoDB: Completed initialization of buffer pool
2015-06-15 09:49:18 3289 [Note] InnoDB: Highest supported file format is Barracuda.
2015-06-15 09:49:19 3289 [Note] InnoDB: 128 rollback segment(s) are active.
2015-06-15 09:49:19 3289 [Note] InnoDB: Waiting for purge to start
2015-06-15 09:49:19 3289 [Note] InnoDB: 5.6.25 started; log sequence number 1677570
2015-06-15 09:49:19 3289 [ERROR] /mysql/bin/mysqld: unknown variable 'log-warings=1'
2015-06-15 09:49:19 3289 [ERROR] Aborting
发现日志已经生效，并且我们写错的参数会告出来重新修改参数启动
[root@localhost mysql]# mysqld_safe --defaults-file=/mysql/my.cnf --user=mysql &
[1] 3687
[root@localhost mysql]# 150615 09:57:59 mysqld_safe Logging to '/mysql/log/mysql.log'.
150615 09:57:59 mysqld_safe Starting mysqld daemon with databases from /mysql/data
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