Sachin Patil

Sachin

Free software developer & Emacser

Qemu - System emulator

In this post I will create an Qemu image and work with it remotely using SSH.

Steps

  1. Download and install qemu from this link.
  2. Create a raw image, install Ubuntu 12.04 from an ISO image.
  3. Boot from an installed image and redirect port 22 to port 2200 of localhost.
  4. Create snapshot of an image.
  5. Booting snapshot image.

Download and install qemu

On Debian based distros(Ubuntu, Mint etc.) install qemu using the command

sudo apt-get install qemu-system

This will install all qemu-system binaries for all major CPU architectures. If you are having RPM based distros(like Redhat, Fedora etc.), type

sudo yum install qemu

Optionally you can also compile qemu from the latest stable source. Please refer the README for compilation instructions.

Create qemu image

We need to first create a raw qemu image using the command

qemu-img create -f raw IMAGE_NAME.img SIZE

For example, if I want to create an image of 32 Gigs with the name ics-testing.img, the command would be

qemu-img create -f raw ics-testing.img 32G

Once the image is created, we can use it as a raw disk image and install an OS(Distro of your choice). In this case I will install ubuntu 12.04 (AMD64) from an ISO image. The syntax would be

qemu-system-ARCH -vnc none,ipv4 -hda IMAGE_NAME -cdrom /PATH/TO/ISO/FILE -m MEMORY -enable-kvm

For example, if my system arch is `x86-64` and my ISO path is /home/psachin/iso/ubuntu-12.04-desktop-amd64.iso with memory as 4 Gigs. Also I want to enable kernel based virtualization.

qemu--system-x86_64 \
    -vnc none,ipv4 \
    -hda ics-testing.img \
    -cdrom /home/psachin/iso/ubuntu-12.04-desktop-amd64.iso \
    -m 4096 \
    -enable-kvm

this will pop up a qemu window. Proceed with the installation and reboot the system.

Boot using qemu image

Once the installation is complete, boot the image by typing,

qemu-system-x86_64 \
    -vnc none,ipv4 \
    -hda ics-testing.img \
    -m 4096 -enable-kvm

Now configure the system, its package manager and user account. Install Openssh-server and enable SSH login. If everything is configured, restart using,

qemu-system-x86_64 \
    -vnc none,ipv4 \
    -hda ics-testing.img \
    -m 4096 \
    -enable-kvm \
    -redir tcp:2200::22

The -redir tcp:2200::22 redirects TCP traffic on the host port 2200 to the guest machine (QEMU) port 22. This allows us to SSH to the port 2200 on localhost.

-vnc none will disable VNC server.

  • SSH to qemu

    You can ssh into the running qemu system using a command

    ssh -p PORT USER@IP-address or HOSTNAME
    

    for example, if I want to connect to port 2200 of localhost with username as qemu-user, then

    ssh -p 2200 qemu-user@localhost
    

    as port 2200 on localhost is open and is binded with port 22 of qemu system, thus we used -p 2200 flag.

Creating snapshots of an image(Optional)

Now as the image is configured and working, we can also create a snapshots of that image and work on it keeping an original image intact.

Syntax:

qemu-img create -f qcow2 -b ORIGINAL_IMAGE_NAME SNAPSHOT_IMAGE_NAME

As my original image name was ics-testing.img, Let my snapshot image name be snapshot.img. Type

qemu-img create -f qcow2 -b ics-testing.img snapshot.img

-f flag will specify image format. In this case it is qcow2 which is most versatile qemu-image format. Please refer man-pages for more detail.

Booting snapshot image

You can use the snapshot image using

qemu-system-x86_64 \
    -vnc none \
    -hda snapshot.img \
    -m 4096 -enable-kvm \
    -redir tcp:2200::22

Tips

a. You can also specify number of CPU cores using -smp flag. For example, if you want to assign 4 cores of your physical system to qemu, specify it as -smp 4. smp stands for Symmetric-multiprocessing.

b. Don’t you run qemu over the snapshot image, it will corrupt the snapshot image.

Refs