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One of the most impressive features of VirtualBox, and virtualization in general, is the ability to run guest operating systems that are completely incompatible with the host operating system. A common requirement in virtualized environments is the sharing of files between the host and guest operating systems. Most virtualization technologies leave this task to the system administrator and, whilst this can be straight forward when the guest virtual machines and host are running the same operating system, it can be become complex when different operating systems are involved. For example, sharing files between a Windows host and a Linux guest involves the installation and configuration of Samba technology and correctly configured network connectivity between the guest and host. 

Fortunately, VirtualBox makes the sharing of files between guests and a host system easy through a feature known as ''Shared Folders''.


== An Overview of VirtualBox Folder Sharing ==

VirtualBox Shared Folders allow files residing on the host system to be accessed by guest operating systems running in virtual machines. In addition, assuming adequate permissions are granted on the shared folder, the guest is also able to transfer files onto the host by copying them into the shared folder. 

VirtualBox folder sharing is currently only supported for Windows and Linux guests. Shared folders are not supported on virtual machines running Windows 3.1, Windows 95, Windows Me or Windows 98 guests.

Shared folders can be configured such that they are persistent (in other words the share is still configured even if the guest is restarted) or transient (such that they a lost after the virtual machine is shutdown or rebooted). Shared folders may also be declared as read-only to prevent the guest operating system from writing to the host folder.

The creation of a shared folder involves selecting the folder on the host system which is be to shared, assigning a share name and choosing whether the folder is to be read-only and transient or permanent.

== Creating Shared Folders on a Powered Off Virtual Machine ==

VirtualBox Shared Folders on inactive virtual machines are configured through the ''Settings'' dialog. This dialog is accessed by selecting the desired virtual machine from the list and clicking the ''Settings'' button in the toolbar. Once the settings dialog is visible, click on the ''Shared Folders'' entry in the right hand pane to display the following screen:


[[Image:virtualbox_shared_folder_settings.jpg|Configuring shared folder settings on a VirtualBox VM]]


To add a new shared folder, click on the add folder button (the top button containing an icon of a folder with a green plus sign) and select a folder on the host system to be shared with the selected guest. To browse for a specific folder, click the down arrow in the ''Folder Path'' text box and select ''Other...'' from the drop down menu. Once a suitable folder has been selected, enter a name for the share in the ''Folder Name'' field. If the guest operating system is to be denied write access to the folder, ensure that the ''Read-only'' check box is selected before clicking the ''OK'' button to create the share:


[[Image:virtualbox_adding_shared_folder.jpg|Adding a shared folder to a virtual machine in VirtualBox]]


Once the shared folder has been configured, start the virtual machine to access the folder. The mechanism for accessing the folder from within the guest will depend on the type of guest operating system running in the virtual machine, details of which are covered later in this chapter.

== Creating Shared Folders for a Running Virtual Machine ==

Shared folders may be configured on a running virtual machine by selecting the ''Devices->Shared Folders..'' menu of the virtual machine window. Once selected, this will display the ''Shared Folders'' dialog as illustrated below:


[[Image:virtualbox_shared_folders_running_vm.jpg|Adding shared folders to a running VirtualBox VM]]


To add a new shared folder, click on the add folder button (the top button containing an icon of a folder with a green plus sign) and select a folder on the host system to be shared with the selected guest. To browse for a specific folder, click the down arrow in the ''Folder Path'' text box and select ''Other...'' from the drop down menu. Once a suitable folder has been selected, enter a name for the share in the ''Folder Name'' field. If the guest operating system is to be denied write access to the folder, ensure that the ''Read-only'' check box is selected. 

If the share is to be transient (in other words it will not be restored when the virtual machine is restarted) leave the ''Permanent'' check box unselected before clicking the ''OK'' button to create the share.

== Accessing a Shared Folder from a Windows Guest ==

On Windows guests, the shared folder should appear as a standard Windows network share listed under ''VirtualBox Shared Folders'', accessible from  the ''Network'' option in the ''Start'' menu. If the shared folder is not visible within the Network window (as can sometime be the case), it may be mapped to a disk drive in a command prompt window by issuing the following command:

net use ''x:'' \\vboxsvr\''ShareName''

where ''x:'' represent the drive letter to be mapped to the shared folder and ''ShareName'' is the name assigned to the shared folder during the creation process outlined above. For example, to map a shared folder named ''TempFiles'' to the S: drive on the guest operating system:

<pre>
C:\Users\vbox> net use s: \\vboxsrv\TempFiles
The command completed successfully.
</pre>

== Accessing a Shared Folder from a Linux Guest ==

Shared Folders are accessed on Linux guests by mounting the folder at a suitable mount point using the ''mount'' command. This can either be an existing directory, or a new directory may be created specifically for this purpose. The syntax to perform the mount (which must be performed as super-user or using the ''sudo'' command) is as follows:

mount -t vboxsf [-o ''MOUNT OPTIONS''] ''ShareName MointPoint''

where [-o ''MOUNT OPTIONS''] represents any optional directives to the mount command, ''ShareName'' is the name assigned to shared folder when it was created and ''MountPoint'' is the path to the directory on the guest where the shared folder is to be mounted. For example, to mount a shared folder named ''TempFiles'' using ''/tmp/mnt'' as the mount point:

<pre>
mkdir /tmp/mnt
mount -t vboxsf TempFiles /tmp/mnt
</pre>

Once this command has been executed, the files in  the host folder will be accessible in /tmp/mnt.