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Mounting a VDI File in a Different VirtualBox Guest

October 17, 2019

Today I wanted to check if a specific file was on an old Linux virtual disk image (VDI) I had on an external backup disk. I had already an Ubuntu guest up and running so I wanted to mount the VDI file located on the external harddisk as an additional virtual harddisk and access it from within the Ubuntu guest.

First, I stopped the Ubuntu guest. Next, I opened the Virtual Media Manager, and added the VDI file.

Adding a VDI file to the Virtual Media Manager

Next, I opened the settings for the Ubuntu guest and selected the storage tab. I selected the SATA controller and clicked the harddisk icon with a green plus symbol to add a new drive. In the dialog window I selected Choose existing disk.

Choosing an existing disk to add to the SATA controller

Next, I started the Ubuntu virtual machine. I used the following command to find the name of the disk:

sudo fdisk -l | grep sd

This command gave the following output for my virtual machine:

Disk /dev/sda: 30 GiB, 32212254720 bytes, 62914560 sectors
/dev/sda1  *     2048 62912511 62910464  30G 83 Linux
Disk /dev/sdb: 50 GiB, 53687091200 bytes, 104857600 sectors
/dev/sdb1  *        2048  88082431 88080384  42G 83 Linux
/dev/sdb2       88084478 104855551 16771074   8G  5 Extended
/dev/sdb5       88084480 104855551 16771072   8G 82 Linux swap / Solaris

The drive added is /dev/sdb and the partition I needed to mount is /dev/sdb1 as /dev/sdb2 is an extended partition with /dev/sdb5 the swap partition.

So, I made a directory to mount the additional virtual harddrive under as follows:

sudo mkdir /old-hdd

Next, I used vi to modify /etc/fstab:

sudo vi /etc/fstab

And added the following to the end of this file:

/dev/sdb1    /old-hdd    ext4    defaults    0    0

After this I could mount the virtual harddisk using:

sudo mount /old-hdd

When I was done with the old virtual harddisk I unmounted it as follows:

sudo umount /old-hdd

And removed the directory I used as a mount point using:

sudo rmdir /old-hdd

And removed the last line from /etc/fstab using vi.

Next, I stopped the virtual machine running Ubuntu so I could remove the virtual harddisk. In the settings for the Ubuntu virtual machine I removed the VDI file from the SATA controller.

Removing the VDI file from the SATA controller

Next, I opened the Virtual Media Manager and with the right VDI file selected I clicked the Remove button. A dialog opened which asked if I wanted to Keep the VDI file or Delete it. As I want to keep this specific VDI around I selected Keep.

Removing the VDI file from the Virtual Media Manager.

Finally, I restarted the Ubuntu virtual machine.