Q:

Set up error logging in mysql server

My mysql server crashes on ubuntu server.  I need to retrieve the logs.  
When doing the following:
    mysql> show variables like '%log%';
I get:
+-----------------------------------------+---------------------------------------+
| Variable_name                           | Value                                 |
+-----------------------------------------+---------------------------------------+
| back_log                                | 50                                    |
| binlog_cache_size                       | 32768                                 |
| binlog_direct_non_transactional_updates | OFF                                   |
| binlog_format                           | STATEMENT                             |
| binlog_stmt_cache_size                  | 32768                                 |
| expire_logs_days                        | 10                                    |
| general_log                             | ON                                    |
| general_log_file                        | /var/log/mysql/mysql.log              |
| innodb_flush_log_at_trx_commit          | 1                                     |
| innodb_locks_unsafe_for_binlog          | OFF                                   |
| innodb_log_buffer_size                  | 8388608                               |
| 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_error                               |                                       |
| log_output                              | FILE                                  |
| log_queries_not_using_indexes           | OFF                                   |
| log_slave_updates                       | OFF                                   |
| log_slow_queries                        | OFF                                   |
| log_warnings                            | 1                                     |
| max_binlog_cache_size                   | 18446744073709547520                  |
| max_binlog_size                         | 104857600                             |
| max_binlog_stmt_cache_size              | 18446744073709547520                  |
| max_relay_log_size                      | 0                                     |
| relay_log                               |                                       |
| relay_log_index                         |                                       |
| relay_log_info_file                     | relay-log.info                        |
| relay_log_purge                         | ON                                    |
| relay_log_recovery                      | OFF                                   |
| relay_log_space_limit                   | 0                                     |
| slow_query_log                          | OFF                                   |
| slow_query_log_file                     | /var/lib/mysql/echidna-music-slow.log |
| sql_log_bin                             | ON                                    |
| sql_log_off                             | OFF                                   |
| sync_binlog                             | 0                                     |
| sync_relay_log                          | 0                                     |
| sync_relay_log_info                     | 0                                     |
+-----------------------------------------+---------------------------------------+
41 rows in set (0.00 sec)

As far as I understand there is no file defined to log the errors, right? 
Even though I have added the following to the my.cnf:
    [mysqld_safe]
    log-error       = /var/log/mysql/err.log
How can I achieve error logging? 

A:

Try moving the 'log-error' definition that you already have under the [mysqld_safe] section to the [mysqld] section
So: 
[mysqld]
log-error = /path/to/log/file

