KVM is a kernel-based Virutal Machine which grows quickly in maturity and popularity in the Linux server market. Red Hat officially dropped Xen in favor of KVM since RHEL 6. With KVM being officially supported by Red Hat, installing KVM on RedHat-based systems should be a breeze.
KVM is a kernel-based Virutal Machine which grows quickly in maturity and popularity in the Linux server market. Red Hat officially dropped Xen in favor of KVM since RHEL 6. With KVM being officially supported by Red Hat, installing KVM on RedHat-based systems should be a breeze.
Preliminary Check - Check Hardware Virtualization Support.
We can check the cpuinfo details to check if our h/w can do VM.
$ egrep -i 'vmx|svm' --color=always /proc/cpuinfo
If CPU flags contain “vmx” or “svm”, it means hardware virtualization support is available. IF NOT THEN DO NOT PROCEED.
Disable SELinux.
Before installing KVM, be aware that there are several SELinux booleans that can affect the behavior of KVM and libvirt. We will set disable in SELinux
# To disable SELinux on CentOS:
$ sudo -e /etc/selinux/config
SELINUX=disabled
Now reboot the server.
Install KVM, QEMU and RPMs/packages.
Install KVM and virtinst (a tool to create VMs).
Install KVM, QEMU and user-space tools.
$ sudo yum install kvm libvirt python-virtinst qemu-kvm
Start libvirtd daemon, and set it to auto-start.
$ sudo service libvirtd start
$ sudo chkconfig libvirtd on
Check if KVM has successfully been installed.
$ sudo virsh -c qemu:///system list
Id Name State
----------------------------------------------------
Also we can do a group install (Optional)
$ sudo yum groupinstall "Virtualisation Tools" "Virtualization Platform"
$ sudo yum install python-virtinst
Configure Linux Bridge for VM Networking.
Installing KVM alone does not allow VMs to communicate with each other or access external networks. We will create a “bridged networking” via Linux bridge.
Install bridge-utils.
Install a package needed to create and manage bridge devices:
$ sudo yum install bridge-utils
Disable Network Manager.
Disable Network Manager service if it’s enabled, and switch to default net manager as follows.
$ sudo service NetworkManager stop
$ sudo chkconfig NetworkManager off
$ sudo chkconfig network on
$ sudo service network start
Create bridge.
To create a bridge we need to configure an active network interface like eth0.
Here we have a static IP assignment.
Note : copy file ifcfg-eth0 as ifcfg-br0, and edit them.
sudo vim /etc/sysconfig/network-scripts/ifcfg-eth0
Add the below lines, we have added a BRIDGE=br0.
DEVICE="eth0"
NM_CONTROLLED="no"
ONBOOT="yes"
TYPE="Ethernet"
BRIDGE=br0
Next we create a bridge br0
sudo vim /etc/sysconfig/network-scripts/ifcfg-br0
Add below lines. Need to look out for - DEVICE, BOOTPROTO, TYPE
DEVICE="br0"
BOOTPROTO="static"
NM_CONTROLLED="no"
ONBOOT="yes"
TYPE="Bridge"
NETMASK=255.255.255.192
IPADDR=10.10.18.36
GATEWAY=10.10.18.1
Now lets restart network
$ sudo service network restart
This will restart the Network. IMPORTANT : make sure we have the bridge configured correctly, else we will loose connectivity if we are on ssh.
[ahmed@zahmed-server ~]$ ifconfig
br0 Link encap:Ethernet HWaddr A0:D3:C1:FA:25:C8
inet addr:10.10.18.36 Bcast:10.130.18.63 Mask:255.255.255.192
inet6 addr: fe80::a2d3:c1ff:fefa:25c8/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2056649 errors:0 dropped:0 overruns:0 frame:0
TX packets:2027594 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:294572910 (280.9 MiB) TX bytes:115946202 (110.5 MiB)
eth0 Link encap:Ethernet HWaddr A0:D3:C1:FA:25:C8
inet6 addr: fe80::a2d3:c1ff:fefa:25c8/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2148683 errors:0 dropped:0 overruns:0 frame:0
TX packets:2030336 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:338047294 (322.3 MiB) TX bytes:136116027 (129.8 MiB)
Interrupt:32
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:6546 errors:0 dropped:0 overruns:0 frame:0
TX packets:6546 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:393148 (383.9 KiB) TX bytes:393148 (383.9 KiB)
virbr0 Link encap:Ethernet HWaddr 52:54:00:C7:5E:B6
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Install VirtManager.
The final step is to install a desktop UI called VirtManager for managing virtual machines (VMs) through libvirt.
To install VirtManager.
$ sudo yum install virt-manager libvirt qemu-system-x86 openss
Launch VirtManager Remotely.
$ sudo yum install xauth
$ sudo vim /etc/ssh/sshd_config
Make sure we have the below line uncommented in sshd_config
X11Forwarding yes
Create wrapper for virt-manager.
Create a following executable wrapper script for virt-manager.
$ sudo -e /usr/bin/vm
Add below lines to the file vm
#! /bin/bash
xauth list | while read line; do
sudo -i xauth add $line
done
sudo -i virt-manager
Let give it exe permissions.
$ sudo chmod +x /usr/bin/vm
Installing vnc-server.
Initial Installation.
Installing base libraries for vncserver to work.
sudo su
yum groupinstall Desktop
Further install
yum install gnome-core xfce4
yum install tigervnc-server
Now make the service on after every reboot
chkconfig vncserver on
Adding VNC user and setting vncpasswd.
Assuming we already have a user on the server ahmed
[root@ahmed-server ~]# su - ahmed
[ahmed@ahmed-server ~]$ vncpasswd
Password:******
Verify:******
[ahmed@ahmed-server ~]$
Now lets configure vncserver
sudo vim /etc/sysconfig/vncservers
Uncomment the line and add as below
VNCSERVERS="2:ahmed"
VNCSERVERARGS[2]="-geometry 1024x768"
Now restart vncserver.
[root@ahmed-server ~]# service vncserver restart
Shutting down VNC server: [ OK ]
Starting VNC server: 2:ahmed xauth: creating new authority file /home/ahmed/.Xauthority
New 'ahmed-server:2 (ahmed)' desktop is ahmed-server:2
Creating default startup script /home/ahmed/.vnc/xstartup
Starting applications specified in /home/ahmed/.vnc/xstartup
Log file is /home/ahmed/.vnc/ahmed-server:2.log
[ OK ]
[root@server1 ~]#
Logging in from Remote machine.
Install vnc-viewer and enter the ip address of ahmed-server followed :2, which is where the vncserver is listing.
10.10.18.36:2
And the password will be the vncpasswd set during the configuration above.
Screenshot.
Troubleshooting KVM and VirtManager setup.
a. If you see the following error when attempting to launch VirtManager remotely, make sure that you use the wrapper script (vm) to launch it, as described above.
X11 connection rejected because of wrong authentication.
Traceback (most recent call last):
File "/usr/share/virt-manager/virt-manager.py", line 383, in
main()
File "/usr/share/virt-manager/virt-manager.py", line 286, in main
raise gtk_error
RuntimeError: could not open display
b. If you see the following D-Bus error:
D-Bus library appears to be incorrectly set up; failed to read machine
uuid: UUID file '/var/lib/dbus/machine-id'
Then run the command below and reboot the host machine.
$ sudo sh -c 'dbus-uuidgen > /var/lib/dbus/machine-id'
c. If you have font issue while running VirtManager, install the following font, and relaunch it.
$ sudo yum install dejavu-lgc-sans-fonts
Upgrade CPU/RAM in KVM.
You can follow the following steps to increase memory size of your KVM virtual machine.
- Update the configuration using command
sudo virsh edit <vm-name> rebootVM server.
Listing virtual servers.
[ahmed@ahmed-server ~]$ sudo virsh list
Id Name State
----------------------------------------------------
8 VM-1 running
12 VM-2 running
13 VM-3 running
15 VM-4 running
Getting Information about VM.
[ahmed@ahmed-server ~]$ sudo virsh dominfo VM-1
Id: 8
Name: VM-1
UUID: 588ff640-25be-9b18-5eb3-f93c471848e6
OS Type: hvm
State: running
CPU(s): 4
CPU time: 503.3s
Max memory: 8388608 KiB
Used memory: 8388608 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: none
Security DOI: 0
Edit Hardware for each VM.
[ahmed@ahmed-server ~]$ sudo virsh edit VM-1
Domain VM-1 XML configuration edited.
Here is now the XML looks like.
Before
<domain type='kvm'>
<name>VM-1</name>
<uuid>588ff640-25be-9b18-5eb3-f93c471848e6</uuid>
<memory unit='KiB'>8388608</memory>
<currentMemory unit='KiB'>8388608</currentMemory>
<vcpu placement='static'>4</vcpu>
<os>
<type arch='x86_64' machine='rhel6.5.0'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
...
...
</domain>
After
<domain type='kvm'>
<name>VM-1</name>
<uuid>588ff640-25be-9b18-5eb3-f93c471848e6</uuid>
<memory unit='KiB'>33554432</memory>
<currentMemory unit='KiB'>33554432</currentMemory>
<vcpu placement='static'>8</vcpu>
<os>
<type arch='x86_64' machine='rhel6.5.0'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
...
...
</domain>
Checking VM information.
[ahmed@ahmed-server ~]$ sudo virsh dominfo VM-1
Id: -
Name: VM-1
UUID: 588ff640-25be-9b18-5eb3-f93c471848e6
OS Type: hvm
State: shut off
CPU(s): 8
Max memory: 33554432 KiB
Used memory: 33554432 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: none
Security DOI: 0
Once this is done restart the server. And we are done.
Interface Changes.
By default VMs take 10M as their transmission speed.
virtio - virtual driver which takes the speed of the bridge (which is 1G).
e1000 - making driver use the 1G speed (this again depends on the Bridge).
Currently have set the speed virtio.
Below are details on how to change it. All command needs to be run on the HOST machine (36) User Command below to change configuration on KVM.
sudo virsh edit <vm_name>
sudo virsh edit VM-1
This will bring up the XML which has the VM configuration which can be changed. Changes with take effect on reboot.
Change Interface Adding <model type='virtio'/> below.
By Default it takes 10M driver.
<interface type='bridge'>
<mac address='52:54:00:60:08:62'/>
<source bridge='br0'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
More Details here : https://help.ubuntu.com/community/KVM/Networking# virtio
Adding HDD to Virtual Machine.
Steps to create virtio HDD.
- First Create a
imageusingqemu-imgcommand. - Add
imageto VM as avirtioHDD. - This will appear as
/dev/vdain the VM, format it using themke2fscommand. - Add to
/etc/fstab, so that the device can be mounted on boot up.
Details below.
First Create a image using qemu-img command.
Below is the command to create image.
[ahmed@ahmed-server ~]# qemu-img create VM-1-NEW-HDD.img 100G
This will create a HDD with 100GB disk.
Add image to VM as a virtio HDD.
Method 1 - Adding image from virt-manager UI.
Steps to Adding from the UI.
- Select a VM,
right-click->open. - Next on the screen select
view->details. - In the new window select
Add Hardware->Storage->select managed or other existing storage.- Select
Device Type:virtio - Select
Storage Format:raw
- Select
After Adding the HDD we can see it as below.
More Info Here : http://unix.stackexchange.com/questions/92967/how-to-add-extra-disks-on-kvm-based-vm
Method 2 - Adding image using virsh command.
To edit the VM configuration use below command.
[ahmed@ahmed-server ~]# virsh edit VM-1
Format
virsh edit <Virtual_Machine_NAME>
To add the image to the server add the below xml tag.
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source file='/virtual_machines/images/VM-1-ADD.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
</disk>
Now reboot the VM, after restart you will see the new device.
[ahmed@ahmed-server ~]# fdisk -l
Added image will appear as /dev/vda in the VM, format it using the mke2fs command.
Before we mount the device we need to format the device.
[ahmed@ahmed-server ~]# mke2fs -j /dev/vda
This will format the device.
Add to /etc/fstab, so that the device can be mounted on boot up.
# /etc/fstab
#
# Column Details here : http://man7.org/linux/man-pages/man5/fstab.5.html
# ------------------------------------------------------------------
/dev/vda /data ext3 defaults 0 0
Now we can check by mounting.
[ahmed@ahmed-server ~]# mount -a
Check by running below command.
[ahmed@ahmed-server ~]# df -h
Useful Links.
- http://xmodulo.com/install-configure-kvm-centos.html
- http://www.cyberciti.biz/faq/kvm-virtualization-in-redhat-centos-scientific-linux-6/
- https://www.howtoforge.com/vnc-server-installation-centos-6.5
- http://wiki.centos.org/HowTos/KVM
- https://www.howtoforge.com/virtualization-with-kvm-on-a-centos-6.4-server-p4
- Redhat Documentation
- http://unix.stackexchange.com/questions/92967/how-to-add-extra-disks-on-kvm-based-vm
- http://www.techotopia.com/index.php/Adding_a_New_Disk_Drive_to_a_CentOS_6_System
- http://blog.zwiegnet.com/linux-server/add-new-hard-drive-to-centos-linux/
- http://man7.org/linux/man-pages/man5/fstab.5.html