Common issues when using virtual machines

In this article:

Common issues when using virtual machines
- Qemu issues
- VMware Player issues
  - Some keyboard keys such as AltGr are ignored by the guest
  - Mouse cursor position offset

Qemu issues

Send the Ctrl-Alt-Del key sequence to the guest

The Ctrl-Alt-Del is a special key sequence intercepted by he operating system. Windows use it as a security¹ measure to unlock its screen, but in the case of virtualized system an alternative is necessary as the key sequence would be intercepted by the host instead of being sent to the guest.

If you are using VNC display, press F8, you should get a menu proposing to send the Ctrl-Alt-Del sequence to the guest.
If accessibility tools are available, enable the on-screen keyboard, press Ctrl-Alt on your physical keyboard and click Del on the on-screen keyboard.
If accessibility tools are not available, on Windows systems press the Shift key at least five times in a row, you should get a pop-up allowing to enable sticky keys. Now successively press the Ctrl, the Alt and then the Del keys to unlock the screen.
Use the command sendkey ctrl-alt-delete in the Qemu Monitor shell. By default this shell can be accessed by pressing Ctrl-Alt-2 (press Ctrl-Alt-1 to go back to guest display), but most Qemu wrapper redirect it. Read the documentation of your particular virtualization software to know how to access the Qemu Monitor shell. With vmtools, use the vmmon(1) command.

Send the Ctrl-*Alt-Fn sequence to nix guests

The Ctrl-Alt-Fn sequence (Where Fn covers function keys usually from F1 to F7) allows to switch from one virtual terminal to another on Unix systems.

When using a text-mode terminal (most common situation when this is needed), some systems also accept the Alt-Right and Alt-Left key sequences to move to the next and previous terminal. As long as these key sequences haven’t been affected to something else in your host desktop environment, they should be forwarded as-is to the guest.
Otherwise you will have to execute sendkey ctrl-alt-fn on the Qemu Monitor shell, see the Ctrl-Alt-Del case above for more details.
Alternatively, if you often need to switch from one terminal to another in text-mode environment, you may want to use a terminal multiplexer such as tmux, the historical screen or the newcomer byobu. Chances are that at least one of those three may be already installed on your system.

The guest does not recognize the network adapter

Qemu and related tools such as GNS3 uses the Intel Gigabit e1000 network adapter by default. This card may not be recognized by some systems, select the Realtek rtl8139 network adapter instead. It is the default adapter selected by the Qemu-KVM project and is usually well recognized by default.

The rtl8139 is a 100 MB/s ethernet adapter, however this shouldn’t really matter as if you really require a fast network access you should switch to virtio (a para-virtualized device) anyway.

Windows 7 remains stuck on the “Starting Windows” screen

For some reason Windows 7 fails to handle standard VGA cards natively (no problem with older systems such as Windows XP or newer ones).

You need to enforce the use of the older cirrus graphical adapter.

The exact procedure depend on the tool you are using. With vanilla Qemu, add the option -vga cirrus. With vmtools, add the option -o vm_display_device=cirrus.

VMware Player issues

Some keyboard keys such as AltGr are ignored by the guest

On some environments, some keys like AltGr may be ignored by the guest.

To solve this, edit the file ~/.vmware/preferences and add the following lines:

xkeymap.keycode.108 = 0x138 # Alt_R
xkeymap.keycode.106 = 0x135 # KP_Divide
xkeymap.keycode.104 = 0x11c # KP_Enter
xkeymap.keycode.111 = 0x148 # Up
xkeymap.keycode.116 = 0x150 # Down
xkeymap.keycode.113 = 0x14b # Left
xkeymap.keycode.114 = 0x14d # Right
xkeymap.keycode.105 = 0x11d # Control_R
xkeymap.keycode.118 = 0x152 # Insert
xkeymap.keycode.119 = 0x153 # Delete
xkeymap.keycode.110 = 0x147 # Home
xkeymap.keycode.115 = 0x14f # End
xkeymap.keycode.112 = 0x149 # Prior
xkeymap.keycode.117 = 0x151 # Next
xkeymap.keycode.78 = 0x46 # Scroll_Lock

Mouse cursor position offset

Sometimes you may have an offset between host’s and the guest’s mouse cursor position.

Using VMware Player in full-screen mode may allow to temporarily solve the issue.

For a more permanent fix, you need to define a fixed screen size in the virtual machine configuration.

This sequence being intercepted by the operating system, requiring it before entering a password makes it hard for a graphical application to fake Windows’ login screen… as long as the user notices the difference with a login prompt not requiring this key sequence at all. ↩

How to build a virtual pentest lab

Standalone virtual machines are both a cheaper and more practical solution to test systems as they doesn’t need to dedicate hardware and are easier to handle than physical installation (actions such as cloning, doing a snapshot or a rollback become trivial).

Network virtualization goes a step further and apply the same system to a whole network, including workstations, servers, and all networking devices such as switches, routers and firewalls. A virtual network can be of any size and topology, and can mimic any real-life situation such as Active Directory domains, remote-access or site-to-site VPNs or test protocols of every network plane.

Such virtual network can be either fully isolated or have one or several link to physical devices and networks, its all up to you to decide.

Hardware

Prerequisites

The goal of a virtual lab is to be able to quickly setup the environment which will allow you to …

Continue

How to run a CAM table overflow attack in GNS3

Knowing where difference with real gears lies

For performance reasons, a lot of switch things are actually not part of the IOS code but are implemented in hardware. This includes the ARL, or Address Resolution Logic, which provides all the methods to add, remove and lookup entries in the MAC address table.

Therefore, for the NM-16ESW module to work in GNS3, Dynamips had to reimplement all these normally hardware provided services, or at least push this far enough to allow an unmodified IOS to run on it correctly.

The sad thing is indeed that this is unfinished work, as stated in this module’s source code header:

/*
 * Cisco router simulation platform.
 * Copyright (c) 2006 Christophe Fillot (cf@utc.fr)
 *
 * NM-16ESW ethernet switch module (experimental!)
 *
 * It's an attempt of proof of concept, so not optimized at all at this …

Continue

vmtools guided tour, part 2: manage virtual machines

Still with me? In this second part of the vmtools guided tour (read the first part first!), we will now enter in the core of the subject and learn how to manage virtual machines, and in particular how virtual machines forks and merges work.

As before, if anything seems unclear or would warrant more explanation, feel free to contact me.

Use `vmcreate` to create virtual machines

Create a virtual machine from an installation ISO image

vmup is useful to boot a virtual disk image, but it doesn’t save the virtual machine settings and does not provide access to vmtools more advanced features.

In vmtools, a virtual machine is a standard directory gathering a few files. To create a new virtual machine, the most common way is to provide the path to the ISO image of an installation disk and the name of a new directory to create:

user@host …

Continue

How to add virtual machines (end devices nodes) in GNS3

Virtual machines can be added in GNS3 topologies as end devices nodes and can play various roles:

Lightweight ones are very focused for instance to provide just enough to test the network connectivity or provide a functional browser.

They start blazingly fast and are very light on resources, meaning you can put several of them to test end-user workstation behavior at several places in your topology with little to no worry about the CPU or memory impact.
Dedicated appliances are designed to provide a specific service, like networking (firewall, …), applicative (proxy, email filtering, …) or administrative (monitoring, …) services.

Resource consumption vary greatly depending on the service and the software used by the appliance. However, professional appliances are usually designed to handle a large number of simultaneous operations: some will support with no issue to see the virtual machine resources settings reduced on test environments (some may require a modification in their …

Continue

vmtools, a Qemu virtual machines manager, is now available

vmtools is a Qemu virtual machines manager which strives to be easy, versatile and modular while adhering to the principle of least privileges, to respect users’ freedom and security.

Easy: Just vmup anything which can be booted, from a local disk image file to remote URLs including .ova archives and devices files. No complex parameters to set or remember, just boots the damn thing.

Virtual machine settings are saved in short and clean plain-text files. No XML, no unneeded settings, only the non-default values specific to the virtual machine, easily readable and editable with any text editor.
Versatile: Use it how you want, vmtools does as few assumptions as possible. No imposed directory structure, no imposed work-flow.

Saved virtual machines are standard directories and files which can be moved, copied or renamed at will, but can also be freely forked and merged to match even advanced work-flows.

vmtools commands offer …

Continue

Popular tags ^{see all}

WhiteWinterWolf Practical IT security, *nix systems & networking