Share files between two SO is easy because there are different protocols for sharing resources (NFS, CIFS/SMB/Samba, FTP, ...), but sharing files between two PCs with OS Linux based, and one of them as virtualmachine guest of another one is a bit more complicated. Here's how to do it when we Mac OSX as HOST and CentOS as GUEST:

Mount DVD ISO image in CentOS VirtualBox guest

1.- Previously, I have download DVD ISO image, then I have copied to my Mac OSX Host.

2.- From Virtual Box menu, goes to Devices > CD/DVD Devices and mount selecting CentOS's DVD ISO image (ISO previuosly added to VBox's "Virtual Media Manager").

3.- In CentOS guest now you can see DVD iso mounted as /media/CentOS_5.5_Final

4.- You can install packages directly off the mounted DVD ISO. Now, modify /etc/yum.repos.d/CentOS-Media.repo file, enter:

[root@localhost ~]# vi /etc/yum.repos.d/CentOS-Media.repo

5.- Make sure enabled is set to 1:

enabled=1

6.- Save and close the file. To install packages from only DVD media repo, do this:

[root@localhost ~]# yum --disablerepo=\* --enablerepo=c5-media -y install <package-name>


Notes:
* --disablerepo=*: disable all yum repo
* -y: assume yes to any question which would be asked
* --enablerepo=c5-media: enable c5-media repo

Install Virtual Box Additions in CentOS guest

Before anything, It is necessary install some packages as compiler gcc, kernel libs and sources.

1.- Install the following packages with CentOS DVD ISO image mounted:

[root@localhost ~]# yum --disablerepo=\* --enablerepo=c5-media -y install gcc
[root@localhost ~]# yum --disablerepo=\* --enablerepo=c5-media -y install kernel sources
[root@localhost ~]# yum --disablerepo=\* --enablerepo=c5-media -y install kernel-devel

2.- Unmount CentOS DVD ISO image and mount Virtual Box Guest Additions in your CentOS guest:

3.- Restart CentOS guest

4.- Now, install VBoxGuestAdditions in CentOS guest:

[root@localhost ~]# cd /media/VBOXADDITIONS_3.2.6_63112/
[root@localhost VBOXADDITIONS_3.2.6_63112]# sh VBoxLinuxAdditions.run

5.- Restart CentOS guest again

6.- Now you could use special functionalities as resize the guest windows, share files, etc...

Share files beetwen Mac OS X as Host and CentOS as Guest

1.- In your Host Linux box:

$ mkdir /Users/chilcano/files2share

2.- In main menu of your Linux Guest's Virtual Box:

  • Go to Devices > Shared Folders ...
  • In popup, add shared folder and select Host's folder (/Users/chilcano/files2share), set up a name as files2share and make permanent.

3.- In your Guest Linux box opens a terminal window and create a new directory where you'll mount shared folder

[root@localhost /]# mkdir /vbox_shared

4.- In this terminal, enter the id command and look the output. We will use uid and gid:

[root@localhost /]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel) context=root:system_r:unconfined_t:SystemLow-SystemHigh

5.- Now, we will mount shared folder from Host to Guest. From terminal in Guest Linux:

[root@localhost /]# mount -t vboxsf -o uid=0,gid=0 files2share /vbox_shared

Make the Mounted Share permanent

You can make the shared folder mount automatically each time you start the CentOS guest by making an entry in /etc/fstab.

1.- From the CentOS guest edit fstab:

[root@localhost ~]# sudo gedit /etc/fstab

2.- Add a line at the bottom of file, and that looks like this:

files2share    /vbox_shared    vboxsf  rw,uid=0,gid=0  0   0

3.- Verify mounted folder

In Mac OS X (host):

In CentOS (guest):

4.- End.

References:

  • CentOS: Install Packages Via yum Command Using DVD / CD as Repo
    http://www.cyberciti.biz/faq/centos-linux-install-packages-from-dvd-using-yum/
  • Implementing virtualbox shared folders between a Mac OS X host and Fedora guest
    http://davidherron.com/content/implementing-virtualbox-shared-folders-between-mac-os-x-host-and-fedora-guest

http://forums.virtualbox.org/viewtopic.php?t=4960&highlight=install+guest+addition
* How to install Guest Additions in CentOS 5.1

  • Share Folders Between a Linux Host and Linux Virtual Machine on VirtualBox
    http://tuxtweaks.com/2009/06/share-folders-linux-host-linux-virtual-machine-virtualbox/