How to Print MySQL Configuration Defaults using mysqldump

The mysqldump command in MySQL is used primarily for creating backups of MySQL databases. One of its options, --print-defaults, allows you to print the default MySQL configuration values that mysqldump would use when executing.

Here are several examples of how you can use mysqldump --print-defaults to understand MySQL’s default configuration:

Example 1: Print the default options without any additional parameters:

    mysqldump --print-defaults
    

This command will output the default options used by mysqldump, such as default host, user, and password configurations.

Example 2: Specify a custom MySQL configuration file to print defaults from:

    mysqldump --defaults-file=/path/to/my.cnf --print-defaults
    

By using --defaults-file, you can specify a different MySQL configuration file to fetch default settings from. This is useful when you have multiple MySQL instances with different configurations.

Example 3: Combine with grep to filter specific default values:

    mysqldump --print-defaults | grep datadir
    

Here, the grep command filters out and displays the default value of the datadir parameter from the MySQL configuration used by mysqldump.

Example 4: Redirect the output to a file for later examination:

    mysqldump --print-defaults > mysql_defaults.txt
    

This command saves all default configuration options into a file named mysql_defaults.txt. You can open this file to inspect or compare defaults over time.

Example 5: Use in a scripting environment to dynamically fetch defaults:

    DEFAULTS=$(mysqldump --print-defaults)
    echo "$DEFAULTS"
    

In scripts, storing the output of mysqldump --print-defaults in a variable (DEFAULTS in this case) allows for further processing or conditional checks based on MySQL’s default settings.

Example 6: Pipe the output to less for easier navigation:

    mysqldump --print-defaults | less
    

Using less enables you to scroll through and search the default MySQL configuration options in a more manageable way, especially if the output is lengthy.

Example 7: Combine with awk to extract specific default values:

    mysqldump --print-defaults | awk '/port/{print $2}'
    

Here, awk filters and prints the default value associated with the port parameter from the mysqldump default configuration.

Example 8: Use tee to both display and save the output:

    mysqldump --print-defaults | tee mysql_defaults.log
    

With tee, you can view the default MySQL configuration options in the terminal while simultaneously saving them to a file (mysql_defaults.log in this case).

Example 9: Check specific default options with sed:

    mysqldump --print-defaults | sed -n '/socket/s/.*=\(.*\)/\1/p'
    

Using sed, this command extracts and displays the default value of the socket option from the mysqldump configuration.

Example 10: Validate the default options against your running MySQL instance:

    mysqldump --print-defaults | mysql --defaults-file=/path/to/my.cnf -N -B -e 'SHOW VARIABLES'
    

By piping the output of mysqldump --print-defaults directly into a mysql command that connects to your MySQL server, you can compare the defaults with the actual configured values in your database.

To verify whether these commands executed successfully, you can check the output displayed in your terminal or the contents of any files they might have created (like mysql_defaults.txt or mysql_defaults.log). Additionally, you can cross-reference the output against the expected default values documented in MySQL’s official resources.