Create a virtual machine on RHEL7 using KVM

The most important step in creating guest os using kvm is creating a bridge network.

1. Create a bridge network

a. Verify whether bridging module network is loaded or not.
Bridging module are loaded on system boot by default. To verify run

# modinfo bridge

b. If the module is not loaded, you can load it using the following command.

# modprobe --first-time bridge

c. Install bridge-utils , if above command fails

# yum install bridge-utils -y

d. Create a file called “ifcfg-virbr0” at location /etc/sysconfig/network-scripts/

# vim /etc/sysconfig/network-scripts/ifcfg-virbr0
DEVICE="virbr0"
BOOTPROTO="static"
IPADDR="192.168.10.25"
NETMASK="255.255.255.0"
GATEWAY="192.168.10.1"
DNS1=192.168.10.2
ONBOOT="yes"
TYPE="Bridge"
NM_CONTROLLED="no"

Modify above file based upon your environment. However ensure that you use NM_CONTROLLED=no

e. Find the ethernet adapter which is having physical network link.

# ifconfig  
It will show list of all the ethernet adapter. 
Usually on a Dell machine 1G adapter have name em1, em2 ... and 10G adapter have names like p4p1, p4p2 etc.
# ethtool em1 | grep "Link detected"
Run this command for all the adapters to find the adapter which have output - Link detected: yes

f. Modify ethernet adapter file that have physical network link.
Here, it is em1.

# vim /etc/sysconfig/network-scripts/ifcfg-em1
DEVICE=em1
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
NM_CONTROLLED=no
BRIDGE=virbr0

f. Restart the network

# systemctl restart network

Troubleshoot: If there is a problem in restarting the network :
— Ensure that all the ethernet adapter files at location /etc/sysconfig/network-scripts/ have NM_CONTROLLED=no
— Move all Ethernet adapter files which do not have uplink to a temp folder

# mkdir /etc/sysconfig/network-scripts/other-network
# mv ifcfg-em2 /etc/sysconfig/network-scripts/other-network
# systemctl restart network

g. Ensure that your bridge network now have the ip address instead on the physical ethernet adapter.
Here, virbr0 should have the ip instead on em1.

# ifconfig

2. Install KVM related package

#yum install qemu-kvm libvirt libvirt-python libguestfs-tools virt-install  virt-manager

3. Start the libvirtd service

# systemctl enable libvirtd
# systemctl start libvirtd

4. Create the virtual machine

For windows guest OS
# virt-install \
   --ram=4096 \
   --vcpus=8 \
   --cdrom=/data/winserver2018.iso \
   --name=winserver2018 \
   --os-type=windows \
   --network bridge=virbr0 \
   --graphics=spice \
   --disk path=/data/vmdisk/winserver2018.qcow2,size=500 \
For linux type guest OS, modify the line 
--os-type=linux.
Modify above command as per your environment.

Thats It!