Creating a qemu system image and working with it using ssh login

In this post I will create a Qemu image and work with it remotely using ssh login.

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 its port 22 to port 2200 of localhost.
  4. Create snapshot of an image.
  5. Booting snapshot image.
  6. Tips.
  7. References.

1. Download and install qemu

If you are having Debian based distro, ubuntu may be, then you can 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 distro(like fedora etc.), first login as root and type 

yum install qemu

else you can also compile the latest stable source. Please refer the README for compilation instructions.

2. Creating and installing image

We need to first create a raw qemu image using command 

qemu-img create -f raw IMAGE_NAME.img SIZE

for example, if I want to create an image of 32G with name as ics-testing.img then 

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. 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 location is /home/devils/iso/ubuntu-12.04-desktop-amd64.iso with memory as 4G. Also I want to enable kernel based virtualisation. 

qemu-system-x86_64 -vnc none,ipv4 -hda ics-testing.img \
-cdrom /home/devils/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.

3. Booting an installed 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’s account. Install Openssh-server and enable ssh logins. If everything is configured, start qemu 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 will allow us to SSH into the machine later by connecting to localhost on port 2200.

-vnc none will disble the vnc server.

  • ssh into 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, so we will use -p 2200 as one of the parameter.

4. Creating snapshots of an image

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

for example if my original image name is ics-testing.img and my snapshot image name is snapshot.img, then 

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.

5. 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

6. 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, then specific it as -smp 4. smp stands for Symmetric-multiprocessing.

b. If you run qemu over the snapshot image, it will corrupt the snapshot image.

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