Change desktop/virtualbox console/command line resolution for linux

Tired of using a little and poor window 640×480 terminal window with your virtualbox/desktop console

First, edit /etc/default/grub and change/uncomment variable GRUB_GFXMODE with your desired value.


Later on, you should also edit /etc/grub.d/00_header and insert “gfxpayload=keep” as seen next:

if loadfont make_system_path_relative_to_its_root ${GRUB_FONT_PATH} ; then
set gfxmode=${GRUB_GFXMODE}
set gfxpayload=keep
insmod gfxterm
if terminal_output gfxterm ; then true ; else
# For backward compatibility with versions of terminal.mod that don’t
# understand terminal_output
terminal gfxterm

If you want to know which resolutions have you got available, you can use hwinfo (hwinfo package in Debian and so)

jack-sparrow:/home/enrgar# hwinfo –framebuffer
02: None 00.0: 11001 VESA Framebuffer
[Created at bios.464]
Unique ID: rdCR.h_b_dKkqAnF
Hardware Class: framebuffer
Model: “NVIDIA MCP79 Board – mcp7a-uo”
Vendor: “NVIDIA Corporation”
Device: “MCP79 Board – mcp7a-uo”
SubVendor: “NVIDIA”
Revision: “Chip Rev”
Memory Size: 14 MB
Memory Range: 0xd1000000-0xd1dfffff (rw)
Mode 0x0300: 640×400 (+640), 8 bits
Mode 0x0301: 640×480 (+640), 8 bits
Mode 0x0303: 800×600 (+800), 8 bits
Mode 0x0305: 1024×768 (+1024), 8 bits
Mode 0x0307: 1280×1024 (+1280), 8 bits
Mode 0x030e: 320×200 (+640), 16 bits
Mode 0x030f: 320×200 (+1280), 24 bits
Mode 0x0311: 640×480 (+1280), 16 bits
Mode 0x0312: 640×480 (+2560), 24 bits
Mode 0x0314: 800×600 (+1600), 16 bits
Mode 0x0315: 800×600 (+3200), 24 bits
Mode 0x0317: 1024×768 (+2048), 16 bits
Mode 0x0318: 1024×768 (+4096), 24 bits
Mode 0x031a: 1280×1024 (+2560), 16 bits
Mode 0x031b: 1280×1024 (+5120), 24 bits
Mode 0x0330: 320×200 (+320), 8 bits
Mode 0x0331: 320×400 (+320), 8 bits
Mode 0x0332: 320×400 (+640), 16 bits
Mode 0x0333: 320×400 (+1280), 24 bits
Mode 0x0334: 320×240 (+320), 8 bits
Mode 0x0335: 320×240 (+640), 16 bits
Mode 0x0336: 320×240 (+1280), 24 bits
Mode 0x033d: 640×400 (+1280), 16 bits
Mode 0x033e: 640×400 (+2560), 24 bits
Mode 0x0345: 1600×1200 (+1600), 8 bits
Mode 0x0346: 1600×1200 (+3200), 16 bits
Mode 0x0347: 1400×1050 (+1400), 8 bits
Mode 0x0348: 1400×1050 (+2800), 16 bits
Mode 0x0349: 1400×1050 (+5600), 24 bits
Mode 0x034a: 1600×1200 (+6400), 24 bits
Mode 0x0352: 2048×1536 (+8192), 24 bits
Mode 0x0360: 1280×800 (+1280), 8 bits
Mode 0x0361: 1280×800 (+5120), 24 bits
Mode 0x0362: 768×480 (+768), 8 bits
Mode 0x0364: 1440×900 (+1440), 8 bits
Mode 0x0365: 1440×900 (+5760), 24 bits
Mode 0x0368: 1680×1050 (+1680), 8 bits
Mode 0x0369: 1680×1050 (+6720), 24 bits
Mode 0x037b: 1280×720 (+5120), 24 bits
Mode 0x037c: 1920×1200 (+1920), 8 bits
Mode 0x037d: 1920×1200 (+7680), 24 bits
Config Status: cfg=new, avail=yes, need=no, active=unknown

Links and references

Compact a VirtualBox Window$ Guest on Debian

If you run Window$ as a virtual machine in a dynamically expanding storage within Debian/Linux using VirtualBox, maybe you’re interested in compact the VDI to save space.

First, you need to download the SDelete application from the Sysinternals web site and extract the zip file in your Window$ drive.
From a command prompt (Start/Run and type ‘cmd‘ to open a command prompt) move to the directory which contains the “sdelete.exe” file and type the followind command:

scdelete -c C:

Shutdown your Windows Guest Machine after fill with zeros the free space in the disk with the previous command and type the following commands from a terminal replacing “MACHINE.vdi” with the name of your VDI:

enrgar@jack-sparrow:~$ VBoxManage modifyhd –compact MACHINE.vdi

Adding as mental note.


Howto to intercommunicate processes in different(remote) machines through DBus


In this post I’m going to try to connect two processes in different machines through DBus. The method is a little bit complex, so be patient if you try.
Also is to advert that this has been the result of 3 days of tests (reference1). So maybe this method may be improved with time and use reference2.

Tools (The actors)

  • dbus
  • gabriel
    • socat
    • libssh
  • ssh
  • your apps

Debian official packages are dbus libssh-2 socat
gabriel is not part of Debian yet (but I’ve build one for myself)

Knowledge (Actors curriculum)

In this section I will describe the basics about the tools we are going to use.

DBus. Extracted from DBus page:

D-Bus is a message bus system, a simple way for applications to talk to one another. In addition to interprocess communication, D-Bus helps coordinate process lifecycle; it makes it simple and reliable to code a “single instance” application or daemon, and to launch applications and daemons on demand when their services are needed.

D-Bus supplies both a system daemon (for events such as “new hardware device added” or “printer queue changed”) and a per-user-login-session daemon (for general IPC needs among user applications). Also, the message bus is built on top of a general one-to-one message passing framework, which can be used by any two apps to communicate directly (without going through the message bus daemon). Currently the communicating applications are on one computer, or through unencrypted TCP/IP suitable for use behind a firewall with shared NFS home directories.

Gabriel is a simple utility to enable D-Bus clients to connect to a D-Bus daemon running on a remote machine, through SSH.
This is the main piece of this puzzle. If you are interested in understanding how it works you should take a look at socat and libssh. As I’ve had to take a look at code, and make some modifications, you should read it as a punishment.

Extracted from socat man page:

socat – Multipurpose relay (SOcket CAT)
socat is a command line based utility that establishes two bidirectional byte streams and transfers data between them. Because the streams can be constructed from a large set of different types of data sinks and sources (see address types), and because lots of address options may be applied to the streams, socat can be used for many different purposes. It might be one of the tools that one ‘has already needed´.

Libssh. Extracted from libssh page:

The ssh library was designed to be used by programmers needing a working SSH implementation by the mean of a library. The complete control of the client is made by the programmer. With libssh, you can remotely execute programs, transfer files, use a secure and transparent tunnel for your remote programs. With its Secure FTP implementation, you can play with remote files easily, without third-party programs others than libcrypto (from openssl).

You should know about ssh and about your application.


Local host will run gabriel and your application.
Remove host will need a running ssh server, a running dbus server and will need socat installed and ready to use.
We need to run gabriel, that will act as a server that will connect our host to the remote host through SSH. After that gabriel will use this SSH connection to intercommunicate our local application with remote DBus applications by using socat.

Remote DBus communication Architecture
Remote DBus communication Architecture

Howto (Main action)

At the moment I’ve only achieved to connect a process using session-bus, I’m still testing until I get connection through system-bus which was my initial purpose.
After reading next information, you will be able to connect using session bus and system bus.

As I commented somewhere else, I’ve made some modifications on gabriel code. I needed some common parameters as SSH port (my virtualbox testing environment ), better help explanations or add a verbose output.
Gabriel establish a connection with the remote ssh and by socat commands it communicates with the remote DBus “environment”. You should administrate ssh parameters and Dbus parameters to gabriel.

We have to put special attention to -d, –bus-address=BUS_ADDRESS because this info must be gotten from the REMOTE machine.
That address is the one used by processes to communicate through DBUS. It’s something “internal” and automatically done when you use DBus api/library. I’m going to show you where to get it.


Again, this info should be gotten from REMOTE machine.
At the moment I don’t know any nice command where to get this info.
We have two main options of DBus buses. System and Session (more info in DBus page).
If you need SESSION bus address, you can choose what it better fits you:

  • You can can get it from process environment
  • You can stole it from any other process suspicious from being involved in DBus activities…
  • You can create your own dbus-daemon (which, actually, I don’t know if it uses it’s own BUS_ADDRESS)

If you need SYSTEM bus address, you can choose what it better fits you:

  • You can can get it from process environment. If it’s not defined, take a look at /etc/dbus-1/system.conf where you should locate a string like <listen>unix:path=/var/run/dbus/system_bus_socket</listen>
  • You can stole it from any other process suspicious from being involved in DBus activities…


This command gives you a dbus-daemon in your session with the one you can contact.

Howto (Main action): Back to local host

Those ugly unix:stri:ngs/asdkaj/numbers we have seen is what we need for -d, –bus-address=BUS_ADDRESS.
See a session example:

See a system example:

The moment we have or gabriel server running we (may have nothing) need to set DBUS_XXX_BUS_ADDRESS. Many apps would use, or have, this environment variable to connect to a DBus instance and intercommunicate with other process.
This is is easy, DBUS_XXX_BUS_ADDRESS should be the address gabriel shows few instants after being launched.
When we have defined this environment variable (in command line) we can execute our app, and it will happily communicate with the remote DBus world.

dbus-browser is a program that uses a session bus.

Curiosity: DBus protocol messages interchanged

Modifying a couple of lines in gabriel can let you see DBus raw protocol messages. It’s a didactic info.
If you enable verbose code at least at level 2, you will get raw DBus protocol messages.

My modifications and hacks

Code will be publish under GLKM project page.

Links and references
  • dbus site
  • gabriel site
  • socat site
  • libssh site
  • reference 1. (informational note, it had implied jumping into gabriel, libssh, and dbus code and testing with a virtualbox machine)
  • reference 2. (personal note, take a look at “Securing traffic between two socat instances using SSL” article in socat page)

Howto access a Virtualbox guest machine throught ssh (or how to port forwarding)

This is not an original article (see references), it’s just an archived one “por si las moscas”.


By default, the network connection in Virtualbox is set to NAT, that is every packet coming from the Guest machine is modified so that it seems as it has come from the Host machine. In this way it’s easy for the Guest machine to connect to all the rest of the network (the Internet included) but nobody can start a connection with the Guest Machine since it’s hidden behind the Host one.

So, if you want to use a server service in your Guest machine (i.e. Apache or SSH) you have two choices:

  1. pass to Virtualbox Host network connection;
  2. make Virtualbox forward all the packets arriving to a certain port of the Host machine.

This article will describe how to do the latter, in particular in the case of the ssh server. This is an interesting case because it allows you to simulate very well a quite common condition: connecting to a remote Linux headless machine.

We have a guest machine with a running ssh server which accepts connections on the TCP port 22.
Our goal is to make any packet arriving at a given TCP port (i.e. 2222) of the host machine, to be forwarded to the TCP port 22 of the guest machine.
Fortunately, there is Virtualbox command which permits to do it almost instantly: VBoxManage.

Configuration needed

In our case we will use Debian as the guest machine name (quote in case guest machine name contains spaces), here are the commands that you have to type in the host machine (real one) console as your user (if you use another user it will try to look for its virtual machines):

user@machine $ VBoxManage list vms
VirtualBox Command Line Management Interface Version 1.5.6_OSE
(C) 2005-2008 innotek GmbH
All rights reserved.
Name: debian
Guest OS: Linux 2.6
UUID: 814e25f4-451e-4582-8d34-71a1cd437cdd
Config file: /mnt/extra/virtualizacion/virtualbox/debian/debian.xml
Memory size: 195MB
user@machine $ VBoxManage setextradata debian “VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort” 2222
VirtualBox Command Line Management Interface Version 1.5.6_OSE
(C) 2005-2008 innotek GmbH
All rights reserved.
user@machine $ VBoxManage setextradata debian “VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort” 22
VirtualBox Command Line Management Interface Version 1.5.6_OSE
(C) 2005-2008 innotek GmbH
All rights reserved.
user@machine$ VBoxManage setextradata debian “VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol” TCP
VirtualBox Command Line Management Interface Version 1.5.6_OSE
(C) 2005-2008 innotek GmbH
All rights reserved.

HostPort,GuestPort,Protocol are just string examples and can be changed without any consequence. Just remember your choices if you want to remove them later.
I guess you should be careful with pcnet substring, as maybe it should have something to see with your selected network card type.


Once you have typed the above commands, you need to close the guest machine (a reboot won’t be sufficient), restart it and then connect via ssh with:

anyuser@machine$ ssh -l >user< -p 2222 localhost

Replace localhost with the host machine ip address if you are connecting from another computer.

By the way, you can check which customizations have been already set for your Guest Machine with VBoxManage by typing:

user@machine$ VBoxManage getextradata debian enumerate
VirtualBox Command Line Management Interface Version 1.5.6_OSE
(C) 2005-2008 innotek GmbH
All rights reserved.
Key: GUI/LastWindowPostion, Value: 0,6,1028,820
Key: GUI/Fullscreen, Value: off
Key: GUI/AutoresizeGuest, Value: off
Key: GUI/LastCloseAction, Value: powerOff
Key: GUI/SaveMountedAtRuntime, Value: yes
Key: GUI/Seamless, Value: off
Key: VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort, Value: 2222
Key: VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort, Value: 22
Key: VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol, Value: TCP

or remove one, for example “VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort”, by setting it without any value:

user@machine$ VBoxManage setextradata “VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort”

Links and references