MySQL log settings and viewing methods

MySQL has the following logs:
Error log: -log-err
Query log: -log
Slow query log: -log-slow-queries
Update log: -log-update
Binary log: –log-bin
By default, all logs are created in the mysqld data directory. By flushing the log, you can force mysqld to close and reopen the log file (or switch to a new log in some cases). A log flush occurs when you execute a FLUSH LOGS statement or when you execute mysqladmin flush-logs or mysqladmin refresh.

1. Error log <br /> Use the --log-error[=file_name] option to specify the location where mysqld saves the error log file. If no file_name value is given, mysqld uses the error log name host_name.err and writes the log file in the data directory. If you execute FLUSH LOGS, the error log is renamed with the suffix -old and mysqld creates a new, empty log file. (If the --log-error option is not given, no renaming will occur.)
If you do not specify --log-error, or (on Windows) if you use the --console option, errors are written to standard error output, stderr. Usually standard output is your terminal.

2. General query log
Start it with the --log[=file_name] or -l [file_name] option. If no value for file_name is given, the default name is host_name.log.

3. Slow query log
When started with the --log-slow-queries[=file_name] option, mysqld writes a log file containing all SQL statements that took longer than long_query_time seconds to execute. If no file_name value is given, it defaults to the host name with the suffix -slow.log. If a file name is given, but not an absolute path name, the file is written to the data directory.

3. Changelog
Starting with the --log-update[=file_name] option is not recommended.

Is logging enabled?
mysql>show variables like 'log_%';
How to know the current log
mysql> show master status;
Displays the number of binary logs
mysql> show master logs;
View binary log files using mysqlbinlog
shell>mysqlbinlog mail-bin.000001
Or shell>mysqlbinlog mail-bin.000001 | tail

Specify the log output location in the configuration file.
Windows: The Windows configuration file is my.ini, which is usually in the MySQL installation directory or c:\Windows.
Linux: The Linux configuration file is my.cnf, which is usually located in /etc.
Under linux:
Sql code
# Enter in [mysqld]
#log
log-error=/usr/local/mysql/log/error.log
log=/usr/local/mysql/log/mysql.log
long_query_time=2
log-slow-queries= /usr/local/mysql/log/slowquery.log
# Enter #log in [mysqld]
log-error=/usr/local/mysql/log/error.log
log=/usr/local/mysql/log/mysql.log
long_query_time=2
log-slow-queries= /usr/local/mysql/log/slowquery.log

Windows:
Sql code
# Enter in [mysqld]
#log
log-error="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/error.log"
log="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/mysql.log"
long_query_time=2
log-slow-queries="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/slowquery.log"
# Enter #log in [mysqld]
log-error="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/error.log"
log="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/mysql.log"
long_query_time=2
log-slow-queries="E:/PROGRA~1/EASYPH~1.0B1/mysql/logs/slowquery.log"

Enable slow query
long_query_time = 2 -- refers to how long the SQL will be logged after it is executed. Here it is 2 seconds
log-slow-queries= /usr/local/mysql/log/slowquery.log --Record the statements that return slower queries
log-queries-not-using-indexes = nouseindex.log -- logs queries that do not use indexes
log=mylog.log --Record all executed statements
Enable mysql log under windows:
Add these under [mysql] (basically adding them at the end):
log-error=
#Enter a name for the query log file. Otherwise a default name will be used.
#Note: (Written as a txt file editplus can be reloaded in time, but sometimes it needs to be placed in the C drive editplus can be reloaded in time)
log= c:/mysql_query.log.txt
#Enter a name for the slow query log file. Otherwise a default name will be used.
log-slow-queries=
#Enter a name for the update log file. Otherwise a default name will be used.
log-update=
#Enter a name for the binary log. Otherwise a default name will be used.
log-bin=