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+How to enable Nested Virtualization in KVM on CentOS 7 / RHEL 7
+======
+**Nested virtualization** means to configure virtualization environment inside a virtual machine. In other words we can say nested virtualization is a feature in the hypervisor which allows us to install  & run a virtual machine inside a virtual server via hardware acceleration from the **hypervisor** (host).
+
+In this article, we will discuss how to enable nested virtualization in KVM on CentOS 7 / RHEL 7. I am assuming you have already configured KVM hypervisor. In case you have not familiar on how to install and configure **KVM hypervisor** , then refer the following article
+
+Let's jump into the hypervisor and verify whether nested virtualization is enabled or not on your KVM host
+
+For Intel based Processors run the command,
+```
+[root@kvm-hypervisor ~]# cat /sys/module/kvm_intel/parameters/nested
+N
+[root@kvm-hypervisor ~]#
+```
+
+For AMD based Processors run the command,
+```
+[root@kvm-hypervisor ~]# cat /sys/module/kvm_amd/parameters/nested
+N
+[root@kvm-hypervisor ~]#
+```
+
+In the above command output 'N' indicates that Nested virtualization is disabled. If we get the output as 'Y' then it indicates that nested virtualization is enabled on your host.
+
+Now to enable nested virtualization, create a file with the name " **/etc/modprobe.d/kvm-nested.conf** " with the following content.
+```
+[root@kvm-hypervisor ~]# vi /etc/modprobe.d/kvm-nested.conf
+options kvm-intel nested=1
+options kvm-intel enable_shadow_vmcs=1
+options kvm-intel enable_apicv=1
+options kvm-intel ept=1
+```
+
+Save & exit the file
+
+Now remove ' **kvm_intel** ' module and then add the same module with modprobe command. Before removing the module, make sure VMs are shutdown otherwise we will get error message like " **modprobe: FATAL: Module kvm_intel is in use** "
+```
+[root@kvm-hypervisor ~]# modprobe -r kvm_intel
+[root@kvm-hypervisor ~]# modprobe -a kvm_intel
+[root@kvm-hypervisor ~]#
+```
+
+Now verify whether nested virtualization feature enabled or not.
+```
+[root@kvm-hypervisor ~]# cat /sys/module/kvm_intel/parameters/nested
+Y
+[root@kvm-hypervisor ~]#
+```
+
+####
+
+Test Nested Virtualization
+
+Let's suppose we have a VM with name "director" on KVM hypervisor on which I have enabled nested virtualization. Before testing, make sure CPU mode for the VM is either as " **host-model** " or " **host-passthrough** " , to check cpu mode of a virtual machine use either Virt-Manager GUI or virsh edit command
+
+![cpu_mode_vm_kvm][1]
+
+![cpu_mode_vm_kvm][2]
+
+Now login to the director VM and run lscpu and lsmod command
+```
+[root@kvm-hypervisor ~]# ssh 192.168.126.1 -l root
+root@192.168.126.1's password:
+Last login: Sun Dec 10 07:05:59 2017 from 192.168.126.254
+[root@director ~]# lsmod | grep kvm
+kvm_intel             170200  0
+kvm                   566604  1 kvm_intel
+irqbypass              13503  1 kvm
+[root@director ~]#
+[root@director ~]# lscpu
+```
+
+![lscpu_command_rhel7_centos7][1]
+
+![lscpu_command_rhel7_centos7][3]
+
+Let's try creating a virtual machine either from virtual manager GUI or virt-install inside the director vm, in my case i am using virt-install command
+```
+[root@director ~]# virt-install  -n Nested-VM  --description "Test Nested VM"  --os-type=Linux  --os-variant=rhel7  --ram=2048  --vcpus=2  --disk path=/var/lib/libvirt/images/nestedvm.img,bus=virtio,size=10  --graphics none  --location /var/lib/libvirt/images/CentOS-7-x86_64-DVD-1511.iso --extra-args console=ttyS0
+Starting install...
+Retrieving file .treeinfo...                                                   | 1.1 kB  00:00:00
+Retrieving file vmlinuz...                                                     | 4.9 MB  00:00:00
+Retrieving file initrd.img...                                                  |  37 MB  00:00:00
+Allocating 'nestedvm.img'                                                      |  10 GB  00:00:00
+Connected to domain Nested-VM
+Escape character is ^]
+[    0.000000] Initializing cgroup subsys cpuset
+[    0.000000] Initializing cgroup subsys cpu
+[    0.000000] Initializing cgroup subsys cpuacct
+[    0.000000] Linux version 3.10.0-327.el7.x86_64 (builder@kbuilder.dev.centos.org) (gcc version 4.8.3 20140911 (Red Hat 4.8.3-9) (GCC) ) #1 SMP Thu Nov 19 22:10:57 UTC 2015
+………………………………………………
+```
+
+![cli-installer-virt-install-command-kvm][1]
+
+![cli-installer-virt-install-command-kvm][4]
+
+This confirms that nested virtualization has been enabled successfully as we are able to create virtual machine inside a virtual machine.
+
+This Concludes the article, please do share your feedback and comments.
+
+--------------------------------------------------------------------------------
+
+via: https://www.linuxtechi.com/enable-nested-virtualization-kvm-centos-7-rhel-7/
+
+作者：[Pradeep Kumar][a]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]:https://www.linuxtechi.com
+[1]:https://www.linuxtechi.com/wp-content/plugins/lazy-load/images/1x1.trans.gif
+[2]:https://www.linuxtechi.com/wp-content/uploads/2017/12/cpu_mode_vm_kvm.jpg
+[3]:https://www.linuxtechi.com/wp-content/uploads/2017/12/lscpu_command_rhel7_centos7-1024x408.jpg
+[4]:https://www.linuxtechi.com/wp-content/uploads/2017/12/cli-installer-virt-install-command-kvm.jpg