mysqldump: flush-privileges option

The documentation is misleading. I read it exactly the same way you do, which isn't what the utility does.

Adding --flush-privileges causes mysqldump to include the following in the backup file, after dumping the mysql schema...

--
-- Flush Grant Tables
--

/*! FLUSH PRIVILEGES */;

...which of course causes the server where the dump is being restored to re-read the potentially-changed grant tables.

And, that's all it does.

Confirmation of this can be found in the source code for mysqldump "10.13" (the version bundled with MySQL Server 5.5.30):

if (flush_privileges && using_mysql_db == 0)
{
  fprintf(md_result_file,"\n--\n-- Flush Grant Tables \n--\n");
  fprintf(md_result_file,"\n/*! FLUSH PRIVILEGES */;\n");
}

The using_mysql_db == 0 comparison was confusing at first, but it turns out to be the return value from a string comparison function where "0" means "identical."

In light of Michael-sqlbot's answer, try to keep one more thing in perspective.

The only time using --flush-privileges is good for a mysqldump is when

• you dump --all-databases (which includes the mysql schema)
• you dump the mysql schema only.

What's even more superficial about the --flush-privileges option for mysqldump is that you can just append the command to the output yourself like this:

mysqldump --all-databases --routines --triggers > MySQLData.sql
echo "FLUSH PRIVILEGES;" >> MySQLData.sql

This assumes you cared to remember this. That's why the --flush-privileges option was added to mysqldump as a reminder.