VirtualBox left side tools is hidden

1. Quit the VirtualBox

2. sudo vim ~/Library/VirtualBox/VirtualBox.xml

Change 

<ExtraDataItem name="GUI/SplitterSizes" value="0,1318"/>

to something like this

<ExtraDataItem name="GUI/SplitterSizes" value="300,1018"/>

3. Start the VirtualBox.

Change the UUID of a Virtual Box .vdi file

To change the UUID of a .vdi file run the following command:

VBoxManage internalcommands sethduuid "full path of your .vdi file"

If you need to change the UUID to a specific UUID then add the UUID at the end :

VBoxManage internalcommands sethduuid "/Users/muktadiur/centos.vdi" "fffd5d63-ac8c-411b-acc8-1d960077fc4e "