MySQL – How to Migrate Database from MySQL 5.7 to MySQL 8.0

Do not mess with the mysql db. There is a lot more going on there than just the users table. Your best bet is the "SHOW GRANTS FOR" command. I have a lot of CLI maintenance aliases and functions in my .bashrc (actually my .bash_aliases that I source in my .bashrc). This function:

mygrants()
{
  mysql -B -N $@ -e "SELECT DISTINCT CONCAT(
    'SHOW GRANTS FOR \'', user, '\'@\'', host, '\';'
    ) AS query FROM mysql.user" | \
  mysql $@ | \
  sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/## \1 ##/;/##/{x;p;x;}'
}

The first mysql command uses SQL to generate valid SQL which is piped to the second mysql command. The output is then piped through sed to add pretty comments.

The $@ in the command will allow you to call it as: mygrants --host=prod-db1 --user=admin --password=secret

You can use your full unix tool kit on this like so:

mygrants --host=prod-db1 --user=admin --password=secret | grep rails_admin | mysql --host=staging-db1 --user=admin --password=secret

That is THE right way to move users. Your MySQL ACL is modified with pure SQL.

A script like this will use the mysql cli client to print out a series of grant statements you would need to use to recreate the user accounts. This command will work best if you have your database credentials stored in you .my.cnf

#!/bin/bash
# adapted from (http://www.pyrosoft.co.uk/blog/2006/10/18/show-grants-for-all-users-on-mysql/)
(
 mysql --batch --skip-column-names -e "SELECT user, host FROM user" mysql 
) | while read user host
do
  echo "# $user @ $host"
  mysql --batch --skip-column-names -e"SHOW GRANTS FOR '$user'@'$host'"
done

If you are jumping from a one version of mysql to another you may want to use this instead of a simply dump of the mysql database. The schema of the mysql database does occasionally get updated.

This will also allow you to pick and choose accounts you want to recreate, if there is some cruft you would like to eliminate.

I was recently using this on a user which included spaces in names, which confused read, since IFS by default includes the space character as a separator. My new and improved command, that seemed to be work better on systems weird usernames.

IFS=$'\t'; while read user host; do
  echo "user:$user host:$host"
  mysql --batch --skip-column-names -e"SHOW GRANTS FOR '$user'@'$host'"
  echo ""
done < <(mysql --batch --skip-column-names -e "SELECT user, host FROM mysql.user")