Can I share MySql database files with Windows on dual boot?

Yes, it works but with some quirks. MySQL uses the same fileformats across platforms so all you need is to share the data directory. One problem is that the data directory need to have mysql as owner and group in ubuntu. And Windows is case-insensitive and Linux is case-sensitive so keep all names uniform: either the whole name lowercase or uppercase but do not mix them.

From start to finish; if you already have things set up this might need some tweaking to fit your setup:

• Install and setup MySQL on both systems.
• Stop the mysql server if it is running.
• Make a new NTFS partition. Mark the device name (let's call it sdXN for now).

• Move the mysql data directory from Ubuntu to the new partition.

  mkdir /{mountpoint}/mysql_data
  sudo mv /var/lib/mysql /{mountpoint/mysql_data
  

  using mv saves permissions.

• Make a new mysql directory

  sudo mkdir /var/lib/mysql
  

• Mount the NTFS partition at /var/lib/mysql. Change the devicename to what it got when you created the NTFS partition.

  sudo mount /dev/{sdXN} /var/lib/mysql -t ntfs-3g -o uid=mysql,gid=mysql,umask=0077
  

• To automount on boot find the partition UUID and locale and edit /etc/fstab.

  ls -l /dev/disk/by-uuid
  locale -a
  sudo gedit /etc/fstab   
  UUID={number_found_with_the_ls-l} /var/lib/mysql ntfs-3g uid=mysql,gid=mysql,umask=0077,locale={your_locale}.utf8  0  0
  

• Change the 'datadir' path in /etc/mysql/my.cnf to point to /var/lib/mysql/mysql_data

• Start the mysql server and test it.

• Edit the Windows config file (my.ini) and set 'datadir' to X:/mysql_data (replace X: for where you mount it under Windows).

Compiled from topic 1442148 on UF.org.

_{I got the Ubuntu version working; so partly untested since I do not have Windows}

If you have added a linux partition to a previously windows-only environment, you can use the database in place with only some minor tweaks. Long version here, short version:

You'll need mount --bind '/media/windows/ProgramData/MySQL/MySQL Server 5.5/data' /var/lib/mysql to run at startup (assuming you mount your windows drive to /media/windows using fstab).

In order to get around innodb's log size checking, you'll need to move the innodb logs for the ubuntu partition. In my.cnf, add innodb_log_group_home_dir = /var/log/mysql so that the logs go next to the mysql error log.