MySQL logging confusion - mysql

Question

I need to turn this on/enable it. I found some info on the net but am very confused now, I don't know where to start.
This is what I have so far. I logged onto MySQL as root and did:
show variables like '%log%';
and got:
Variable_name | Value |
+---------------------------------+----------------------------------+
| back_log | 50 |
| binlog_cache_size | 32768 |
| binlog_format | STATEMENT |
| expire_logs_days | 10 |
| general_log | ON |
| general_log_file | /var/lib/mysql/helloise.log |
| innodb_flush_log_at_trx_commit | 1 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_buffer_size | 1048576 |
| innodb_log_file_size | 5242880 |
| innodb_log_files_in_group | 2 |
| innodb_log_group_home_dir | ./ |
| innodb_mirrored_log_groups | 1 |
| log | ON |
| log_bin | OFF |
| log_bin_trust_function_creators | OFF |
| log_bin_trust_routine_creators | OFF |
| log_error | /var/log/mysql/error.log |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_queries | OFF |
| log_warnings | 1 |
| max_binlog_cache_size | 4294963200 |
| max_binlog_size | 104857600 |
| max_relay_log_size | 0 |
| relay_log | |
| relay_log_index | |
| relay_log_info_file | relay-log.info |
| relay_log_purge | ON |
| relay_log_space_limit | 0 |
| slow_query_log | OFF |
| slow_query_log_file | /var/lib/mysql/helloise-slow.log |
| sql_log_bin | ON |
| sql_log_off | OFF |
| sql_log_update | ON |
| sync_binlog | 0
I did: SET GLOBAL general_log = 1 to set general_log = ON. Will all queries be logged in /var/lib/mysql/helloise.log?
And when I try to access the mysql directory via helloises#helloise:/var/lib$ cd mysql/ I get permission denied
and then I also have a log directory:
helloises#helloise:/var/log$
with a whole lot of log files ex: mysql.log
Which log file will contain my queries so I can track what my db is doing and see how long queries take?

Answer 1

Firs of all you got a permission denied because you hav not the privileges to read it. Try a
ls -l
on that file and see what permission are defined. Then yuo can use chmod to change permissions. Or simply try to read that file as a root user.
The general log is a logging feature for query log, reading, from guide:
The general query log is a general record of what mysqld is doing. The
server writes information to this log when clients connect or
disconnect, and it logs each SQL statement received from clients. The
general query log can be very useful when you suspect an error in a
client and want to know exactly what the client sent to mysqld.
The error log:
The error log contains information indicating when mysqld was started
and stopped and also any critical errors that occur while the server
is running. If mysqld notices a table that needs to be automatically
checked or repaired, it writes a message to the error log.
For understand the differences i suggest you to read that site:
http://dev.mysql.com/doc/refman/5.1/en/server-logs.html
The file that contains the queries is the one in /var/lib/mysql/helloise.log
For the slow query logs you can check:
http://dev.mysql.com/doc/refman/5.1/en/slow-query-log.html
it logs all the query that take more time than long_query_time seconds (that variable must be defined by yourself). I don't found a way to show the execution time of a query, but check that page http://dev.mysql.com/doc/refman/5.1/en/log-destinations.html it could help you on how to configure general/slowquery logging.
Hope this help.