Sometimes you want to download a torrent that you’ve partially downloaded. Many bittorrent client allow partially downloaded files, but what if you’ve downloaded the same torrent twice, with differents parts available?

Use Zeroconf / Local peer

I’ve used two client on the same LAN, ktorrent (on Debian) and utorrent (on Windows XP). I’ve two downloaded files (or folder) from the same .torrent, with different parts downloaded.

• Enable Zeroconf plugin on ktorrent
• Check if on utorrent “Enable local peer discovery” is enabled
• Import existing download #1 on ktorrent
• On debian system, as root type ifconfig to discover your local IP address, i.e.  inet addr:192.168.0.XX
• Go to ktorrent preferences and check the used port (e.g. 12345)
• On utorrent go to Peers tab on #2 download. Right-click > Add peer
• Type your first machine IP address (e.g. Debian) and the first bittorrent client port (e.g. 12345 on ktorrent),  e.g. 192.168.0.XX:12345 with no protocol prepended.

On both client you’ll notice a new peer, downloading and uploading very fast. Little after, the two downloaded files / folder could be completely merged.

You can now close #2 and continue to download the torrent on a single machine / client from external peers.

Note: I’ve tested this method on the same machine using Virtualbox (Debian as host, XP as guest).

See also:

• Merge / combine a torrent

Host: Debian GNU/Linux
Guest: Windows XP

Read the user manual on Folder sharing section.

1. Install Guest Additions (Devices > Install Guest Additions)
2. Click on folder icon on the bottom of the VirtualBox
3. Create a new shared folder: select a directory on Host and choose a name (e.g. my_shared_folder)
4. On a command shell (cmd) type this command
   net use x: \\vboxsrv\my_shared_folder

Where x: is a free device letter.

Tested under:

• GNU/Linux distro: Debian lenny/sid
• Kernel: 2.6 (2.6.22-3-k7)
• Architecture: AMD K7 (Athlon XP 1900+)

Prerequisites: make sure you’ve selected both lenny and sid repositories. In your /etc/apt/sources.list you must read something like this:

## Debian Unstable (sid)
deb http://ftp.it.debian.org/debian/ sid main contrib non-free
deb-src http://ftp.it.debian.org/debian/ sid main contrib non-free
## Debian Testing (lenny)
deb http://ftp.it.debian.org/debian/ lenny main contrib non-free
deb-src http://ftp.it.debian.org/debian/ lenny main contrib non-free

You can also add the Virtual Box repository:

##VIRTUALBOX
deb http://www.virtualbox.org/debian etch non-free
deb http://download.virtualbox.org/virtualbox/debian lenny non-free

But achtung! It’s the Evil Proprietary Version.

In this howto, I install the VirtualBox OSE (Open Source Editon) available in Debian repositories.

1. # apt-get update (necessary if you changed /etc/apt/sources.list)
2. # apt-get install virtualbox-ose virtualbox-ose-source virtualbox-ose-modules-2.6-k7 virtualbox-ose-guest-utils virtualbox-ose-guest-source Note: virtualbox Guest Additions should be installed only if you’re running a linux distro within a virtualbox (such a virtual machine is called “guest”)Change virtualbox-ose-modules-2.6-XXX with your architecture (486,686 ecc.). The 486 version is installed by default. This is a meta-package that download the latest version of virtualbox for 2.6 kernel on specified architecture.
3. After installation, in order to run VirtualBox, you have to plug a kernel module named vboxdrv specific for your kernel. To do this:
   1. # apt-get install module-assistant
   2. # m-a prepare
   3. # m-a a-i virtualbox-ose If you’ve installed the binary version from virtualbox.org, specify virtualbox instead virtualbox-ose
   4. # modprobe vboxdrv

   During module-assistant auto-install (m-a a-i) of vboxdrv module, kernel headers of the running kernel are used to create the module. Then modprobe add plug vboxdrv to the running kernel. If something going wrong in this phase, follow the on screen instruction from the module assistant. Make sure you’ve downloaded the right kernel headers (module assistant should automatically do this, i.e. installing linux-headers-2.6.22-3-k7 for linux-image-2.6.22-3-k7), elsewhere module build cannot be completed.

4. Now you can try to run virtualbox-ose. After you’ve created and run a virtual machine, you can get a message asking you to check dmesg. Open a root shell and type dmesg | grep vbox. The error message ask you to add a kernel command line about NMI watchdog. If it’s your case, do this:
   1. # gedit /boot/grub/menu.lst
   2. Find a line like kopt=... and add, before all, the required command: nmi_watchdog=0 and save. DO NOT uncomment the line, update-grub make the dirty job for you.
   3. # update-grub
   4. Reboot
5. Reading the dmesg, you find:

   $ dmesg | grep vbox
   vboxdrv: Trying to deactivate the NMI watchdog permanently...
   vboxdrv: Successfully done.

   This meant that NMI issue is solved.

6. Now you can run successfully the virtual machine. Enjoy virtualization!

After installation:

The vboxusers group

If you want to allow your unprivileged user to use virtualbox, do:
# sudo adduser `whoami` vboxusersAdd to vboxusers group any other user you want to use this.

Install VirtualBox Guest Additions on Guest

If you want to enable some advanced features, like mouse and screen resolution tweaks, you’ve to install VirtualBox Guest Additions in the guest virtual machine. If you run a Windows virtual machine, you can get the precompiled (.exe) installer from this dedicated Google Code projectAfter you reboot guest, VirtualBox enable the advanced functionalities, like seamless mode for mouse pointer and a wide range of resolution and colors for the emulated VM video card.

Update: Well, you can also download Guest Additions from the dropdown menu (Devices) of a running guest. You’ll get a CD image to mount on virtual machine with all the packages you’ve to install.
Note: Virtualbox guest additions on the “host” (real) machine has no effect: if during boot you get the “Not in a virtual machine” error from guest additions, it simply means that your OS run on a host machine, not in a guest one.

See also:

• Supported Guest OS comparison
• User FAQ
• Download End-User Manual and virtualbox software
• More Virtualbox HOWTOs