Check the configuration before starting the MySQL server

MySQL Server supports the validate-config option, which allows checking the startup configuration for problems without starting the server in normal operation mode:

• If no errors are found, the server terminates with the output code 0.
• If an error is found, the server displays a diagnostic message and terminates with output code 1.

Valate-config can be used at any time, but is especially useful after an upgrade to check if any options previously used with an older server, an upgraded server are considered obsolete or outdated.

MySQL version and configuration

First let’s have some information about my MySQL version and configuration.

$ mysqld --help --verbose | head -n13
mysqld Ver 8.0.16 for Linux on x86_64 (MySQL Community Server - GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its affiliates.
affiliates. Other may be trademarks of their respective
owners.

Starts the MySQL database server.

Usage: mysqld [OPTIONS].

Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf

We use MySQL server 8.0.16

The default configuration of the parameters is read in the specified order from:

/etc/my.cnf
/etc/mysql/my.cnf
/usr/local/mysql/etc/my.cnf
~ / .My.cnf

Now let’s check the start-up configuration of my MySQL server:

$ mysqld --validate-config
$

No error ! No output, everything looks good. Our server will start with this configuration. In case of an error the server will shut down.

The output is clearly different:

$ mysqld --validate-config --fake-option
2019-06-05T15:10:08.653775Z 0 [ERROR] [MY-000068] [Server] unknown option '--fake-option'.
2019-06-05T15:10:08.653822Z 0 [ERROR] [MY-010119] [Server] Aborting

Usually your configuration settings are written in your configuration file (usually with the name my.cnf).

So you can also use validate-config in this context:

$ mysqld --defaults-file=/etc/my.cnf --validate-config
$

Note:

1. defaults-file, if specified, should be the first parameter on the command line.
2. Alternatively, you can handle verbosity using log_error_verbosity:

• A value of 1 gives you an ERROR
• A value of 2 gives you ERROR and WARNING.
• A value of 3 gives you an ERROR, WARNING AND INFORMATION (i.e. a note).

With a value of 2, in addition to errors, we will be able to display warnings:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
2019-06-05T15:53:42.785422Z 0 [Warning] [MY-011068] [Server] The syntax 'expire-logs-days' is deprecated and will be removed in a future release. Please use binlog_expire_logs_seconds instead.
2019-06-05T15:53:42.785660Z 0 [Warning] [MY-0101] [Server] Insecure configuration for --secure-file-priv: Location is accessible to all OS users. Consider choosing a different directory.

Nothing particularly serious, but it is recommended to remove the warnings if possible.

Therefore, we have fixed these warnings:

Use binlog_expire_logs_seconds instead of expire-logs-days
Set the correct permissions for your secure-file-priv directory
$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
2019-06-05T16:04:32.363297Z 0 [ERROR] [MY-000067] [Server] unknown variable 'binlog_expire_logs_second=7200'.
2019-06-05T16:04:32.363369Z 0 [ERROR] [MY-010119] [Server] Aborting

Sorry !!! There is a misprint …: -0
We wrote binlog_expire_logs_second instead of binlog_expire_logs_seconds. (We forgot the last “s”). In this case my MySQL server cannot start.

Thanks to validate-config ! Now we can avoid unpleasant sensations when starting the server. If written correctly, we now have no errors or warnings:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
$

Note that you can also use value 3:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=3
2019-06-05T16:02:03.589770Z 0 [Note] [MY-010747] [Server] Plugin 'FEDERATED' is disabled.
2019-06-05T16:02:03.590719Z 0 [Note] [MY-010733] [Server] Shutting down plugin 'MyISAM'.
2019-06-05T16:02:03.590763Z 0 [Note] [MY-010733] [Server] Shutting down plugin 'CSV'

It is convenient and can be very useful. It may be worth including it in the update process.

Note:

1. Defaults-file, if specified, should be the first parameter on the command line.
2. Alternatively, you can handle verbosity using log_error_verbosity:

• A value of 1 gives you an ERROR
• A value of 2 gives you ERROR and WARNING.
• A value of 3 gives you an ERROR, WARNING AND INFORMATION (i.e. a note).

With a value of 2, in addition to errors, we will be able to display warnings:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
2019-06-05T15:53:42.785422Z 0 [Warning] [MY-011068] [Server] The syntax 'expire-logs-days' is deprecated and will be removed in a future release. Please use binlog_expire_logs_seconds instead.
2019-06-05T15:53:42.785660Z 0 [Warning] [MY-0101] [Server] Insecure configuration for --secure-file-priv: Location is accessible to all OS users. Consider choosing a different directory.

Nothing particularly serious, but it is recommended to remove the warnings if possible.

Therefore, we have fixed these warnings:

• Use binlog_expire_logs_seconds instead of expire-logs-days
• Set the correct permissions for your secure-file-priv directory

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
2019-06-05T16:04:32.363297Z 0 [ERROR] [MY-000067] [Server] unknown variable 'binlog_expire_logs_second=7200'.
2019-06-05T16:04:32.363369Z 0 [ERROR] [MY-010119] [Server] Aborting

Sorry !!! There is a misprint …: -0
We wrote binlog_expire_logs_second instead of binlog_expire_logs_seconds. We forgot the last “s”. In this case my MySQL server cannot start. Thanks to validate-config! Now we can avoid unpleasant sensations when starting the server.

If written correctly, we now have no errors or warnings:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=2
$

Note that you can also use value 3:

$ mysqld --defaults-file=/etc/my.cnf --validate-config --log_error_verbosity=3
2019-06-05T16:02:03.589770Z 0 [Note] [MY-010747] [Server] Plugin 'FEDERATED' is disabled.
2019-06-05T16:02:03.590719Z 0 [Note] [MY-010733] [Server] Shutting down plugin 'MyISAM'.
2019-06-05T16:02:03.590763Z 0 [Note] [MY-010733] [Server] Shutting down plugin 'CSV'

It is convenient and can be very useful. It may be worth including it in the update process.