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Leon Nunes
Leon Nunes

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Creating a compressed and minimal KVM template

#kvm #linux #qemu #guide

Note❗: This is purely for self-learning, so that I can learn how to automate my Virtual Machines using Libvirt

Goal 

 virt-sysprep virt-sysprep (reset) (add user, keys, logos) | | dd v dd v original guest ----> template ---------> copied ------> custom template guest
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To start this you first need to install a virtual machine in KVM, either by using virt-install or virt-manager. Automating this is possible via kickstart or by downloading a cloud image, I did it manually.

This was the base image after installation and it was around 2.1 GB on disk and 10GB virtually.

qemu-img info "rocky-linux.qcow2" file format: qcow2 virtual size: 10 GiB (10737418240 bytes) disk size: 2.25 GiB
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I've used virt-sparsify instead of dd with compress which made the image size 1GB on disk and took around 5 minutes for it to complete

sudo virt-sparsify --tmp=./ --compress rocky-linux.qcow2 rocky-linux-template.qcow2
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Final file “rocky-linux-template.qcow2” which is 1GB 🔥.

sudo qemu-img info rocky-linux-template.qcow2 virtual size: 10 GiB (10737418240 bytes) disk size: 0.993 GiB
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Now let’s virt-sysprep it

sudo virt-sysprep -a rocky-linux-template.qcow2
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Time to virt-sparsify it again

sudo virt-sparsify --tmp=./ --compress rocky-linux-template.qcow2 rocky-linux-g1.qcow2
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Time to add the ssh keys and relabel the system

sudo virt-sysprep --format=qcow2 -a rocky-linux-g1.qcow2 \ --ssh-inject root:file:.ssh/id_rsa.pub \ --selinux-relabel --hostname rk-g1-minimal
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Creating a guest out of this

 virt-install --connect qemu:///system \ --name "${VM_NAME}" \ --disk "${VM_DISK_PATH}",target.bus=virtio \ --boot hd \ --memory=1048 \ --noautoconsole \ --graphics none \ --os-variant "${VM_OS_VARIANT}" \ --vcpus 2 \ --cpu host \ --os-type linux \ --network network=br0,model=virtio \ --console pty,target_type=serial
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And it’s done ✌️

Top comments (2)

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noobyco profile image
Md Moinuddin • • Edited

Nedda explore this, getting FOMO... how could I miss exploring this aggghhh!!!

Thanks for steps Leon :)))

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mediocredevops profile image
Leon Nunes •

hahahaha you can still do it, at that time nobody used to look at KVM in this way :p