KVM (Kernel-based Virtual Machine) is a virtualization infrastructure for the Linux kernel that turns it into a hypervisor.
Installing
## check hardware virtualization supoort $ egrep -i 'vmx|svm' --color=always /proc/cpuinfo ## disable SELinux $ vi /etc/selinux/config SELINUX=permissive $ reboot ## install KVM, QEMU and user-space tools $ apt-get install qemu-kvm qemu-utils libvirt-bin | yum install qemu-kvm qemu-img libvirt $ sudo service libvirtd start | sudo systemctl start libvirtd # optionally add yourself to libvirtd group, otherwise sudo $ sudo adduser <youruser> libvirtd # check libvirtd daemon $ sudo virsh -c qemu:///system list
from kvm@debian and kvm@centos
Networking
libvirt installation provides NAT based connectivity, also called default virtual network. It adds iptables rules to allow traffic to/from guests attached to the virbr0 device in the INPUT, FORWARD, OUTPUT and POSTROUTING chains, and attempt to enable ip_forward.
Advanced users will want to use full bridging, where the guest is connected directly to the LAN. Don’t attach a physical device to virbr0 (this is only for NAT connectivity).
## check default NAT virtual network $ virsh net-list --all default active yes $ brctl show virbr0 ## bridging non-persistent using bridge-utils/brctl $ apt-get|yum install bridge-utils $ brctl addbr br0 $ brctl addif br0 eth0 # assign ip to bridge $ ip link set dev br0 up $ ip addr add dev br0 10.10.1.105/24 # delete $ ip link set dev eth0 promisc on $ ip link set dev eth0 master br0 ## bridging using ifcfg/rhel # disable network manager $ sudo service NetworkManager stop ; sudo chkconfig NetworkManager off $ sudo chkconfig network on ; sudo service network start $ ifdown eth0 $ vi /etc/sysconfig/network-scripts/ifcfg-eth0 DEVICE=eth0 TYPE=Ethernet ONBOOT=yes NM_CONTROLLED=yes BRIDGE=br0 $ vi /etc/sysconfig/network-scripts/ifcfg-br0 DEVICE=br0 NM_CONTROLLED=yes ONBOOT=yes TYPE=Bridge # either static BOOTPROTO=none IPADDR=10.10.1.105 NETMASK=255.255.255.0 GATEWAY=10.10.1.1 DNS1=8.8.8.8 DNS2=8.8.4.4 # or dhcp #BOOTPROTO=dhcp $ ifup eth0 ; ifup br0 ## bridging in debian $ vi /etc/network/interfaces #auto eth0 #iface eth0 inet dhcp # either static iface br0 inet static bridge_ports eth0 eth1 address 10.10.1.105 broadcast 10.10.1.255 netmask 255.255.255.0 gateway 10.10.1.1 # or dhcp auto br0 iface br0 inet dhcp bridge_ports eth0 bridge_stp off bridge_fd 0 bridge_maxwait 0 $ /etc/init.d/networking restart ## bridging using nmcli/networkmanager $ nmcli con add type bridge autoconnect yes con-name br0 ifname br0 # either static $ nmcli con mod br0 ipv4.addresses "10.10.1.105/24 10.10.1.1" ipv4.method manual $ nmcli con mod br0 ipv4.dns "8.8.8.8 8.8.4.4" # or dhcp $ nmcli con mod br0 ipv4.method auto # remove current setting and add interface to bridge $ nmcli c delete eth0 $ nmcli c add type bridge-slave autoconnect yes con-name eth0 ifname eth0 master br0 $ systemctl restart NetworkManager
from virtual networking and networking hints and tips
Using virsh
Virsh/virsh@man is main interface for managing (create, pause shutdown) virsh guest domains. It uses libvirt@wiki, an open source C API/lib, daemon and management tool for managing platform virtualization. It can be used to manage KVM, Xen, LXC, VMware ESX, QEMU, VirtualBox, Hyper-V, Bhyve and other virtualization technologies.
$ curl http://cdimage.ubuntu.com/ubuntu-server/daily/current/vivid-server-amd64.iso
-o linux.iso
## create virtual disk using qcow2 (grows as needed)
$ qemu-img create -f qcow2 /var/lib/libvirt/images/guest.qcow2 8G
## create domain xml file either manually
$ uuid
f5b8c05b-9c7a-3211-49b9-2bd635f7e2aa
$ vi guest.xml
<domain type='kvm'>
<name>guest</name>
<uuid>f5b8c05b-9c7a-3211-49b9-2bd635f7e2aa</uuid>
<memory>1048576</memory>
<currentMemory>1048576</currentMemory>
<vcpu>2</vcpu>
<os>
<type>hvm</type>
<boot dev='cdrom'/>
</os>
<features>
<acpi/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>
<devices>
<emulator>/usr/bin/kvm</emulator>
<disk type="file" device="disk">
<driver name="qemu" type="qcow2"/>
<source file="/var/lib/libvirt/images/guest.qcow2"/>
<target dev="vda" bus="virtio"/>
<address type="pci" domain="0x0000" bus="0x00" slot="0x04" function="0x0"/>
</disk>
<disk type="file" device="cdrom">
<driver name="qemu" type="raw"/>
<source file=linux.iso"/>
<target dev="hdc" bus="ide"/>
<readonly/>
<address type="drive" controller="0" bus="1" target="0" unit="0"/>
</disk>
<controller type="ide" index="0">
<address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x1"/>
</controller>
<input type='mouse' bus='ps2'/>
<graphics type='vnc' port='-1' autoport="yes" listen='127.0.0.1'/>
<console type='pty'>
<target port='0'/>
</console>
</devices>
</domain>
## start vm
$ virsh create guest.xml
$ virsh list
...
## remote access vm
# either by vnc, usually kvm-host:5900
$ sudo netstat -nap | grep kvm
tcp 0 0.0.0.0:5900
# or console
$ virsh console guest
## manage VMs
$ virsh destroy|shutdown|undefined|suspend|resume|autostart guest
Using virt-install
virt-install@man is a command line tool for creating new KVM , Xen, or Linux container guests using libvirt
## install $ apt-get install virtinst | yum install virt-install '-r,--ram MEMORY' guest memory '--vcpus VCPUS' guest virtual cpus '--cpuset CPUSET' physical cpus used by guest, eg: 1-5,^3,8 '-c,--cdrom CDROM or' virtual file or device, iso usually '--boot=BOOTOPTS' boot priority and kernel args, eg: cdrom,fd,hd,network,kernel_args="console=/dev/ttyS0" '--disk path=PATH,size=G,format=raw|qcow2' same as '--filesystem PATH' guest storage media, created if doesnt exist '--network bridge=BRIDGE|network=NAME' '--graphics vnc|none' defaults to vnc '--hvm' request full virtualization, useful if both para and full virtualizations are available '--autostart' start domain on host boot ## start VM (from ISO locally or remotelly) $ virt-install --name guest --ram 1024 --vcpus=2 --disk path=/var/lib/libvirt/images/guest.qcow2,device=disk,size=8 --network bridge=virbr0 --cdrom linux.iso
from Installing a virtual machine using virt-install and virt-install@tecmint
Using guestfish/libguestfs
libguestfs/Libguestfs@wiki/guestfish@man is a set of tools for accessing and modifying virtual machine (VM) disk images. You can use this for viewing and editing files inside guests, scripting changes to VMs, monitoring disk used/free statistics, creating guests, P2V, V2V, performing backups, cloning VMs, building VMs, formatting disks, resizing disks, and much more.
Libguestfs is a C library. All this functionality is available through guestfish scriptable and interactive shell, or virt-* tools (just a script wrapper).
## install $ apt-get install libguestfs-tools | yum install libguestfs-tools | yaourt -S libguestfs '-rw(default) or -ro' read-write or read-only '-d libvirt-domain or -a disk.img' '-i' interactive shell # list files $ virt-ls -d DOMAIN DIRECTORY # edit file $ virt-edit -d DOMAIN FILE -e 'SED-EXPR' $ guestfish --rw -i -d DOMAIN ><fs> download FILE /tmp/FILE ><fs> ! sed -i 'SED-EXP' /tmp/FILE ><fs> upload /tmp/FILE FILE # remove root password $ virt-edit -a disk.img /etc/passwd -e 's/^root:.*?:/root::/' # checksum file $ guestfish --ro -a disk.img -i checksum sha256 FILE # convert ISO to tarball $ guestfish --ro -a in.iso -m /dev/sda tgz-out / out.tar.gz # interactive commands, eg: delete,touch,stat a file $ guestfish -a disk.img -i rm FILE $ guestfish --ro -a disk.img -i stat FILE # list all commands $ guestfish -h # lists differences between files in two VMs (or disk images) $ virt-diff -d oldguest -D newguest $ virt-diff -a old.img -A new.img # disable systemd service $ guestfish -a disk.img -i ln-sf /dev/null /etc/systemd/system/cloud-init.service # export directory from VM $ virt-copy-out -d DOMAIN VMDIR LOCALDIR # read file $ virt-cat disk.img FILE # install packages $ virt-builder fedora-20 -edit '/etc/yum.repos.d/fedora-updates-testing.repo:s/enabled=0/enabled=1/' --install emacs # list os/templates supported $ virt-builder --list # same but using virt-customize $ virt-customize -a fedora-20.img --update --install gcc # show free space $ virt-df -a disk.img # list all filesystems $ virt-filesystems -a disk.img --all --long -h # show OS info, including version and installed packages $ virt-inspector -d DOMAIN # create a new image $ virt-builder centos-7.0 # set root password $ virt-sysprep --enable customize --root-password password:123456 -a /dev/sdX # resize image, expand '/dev/sda2' by '+5G' $ virt-filesystems --long -h --all -a olddisk $ truncate -r olddisk newdisk ; truncate -s +5G newdisk $ virt-resize --expand /dev/sda2 olddisk newdisk
from virt-tools, virt-tools@rwmj and guestfs-recipes/guestfs-recipes@ubuntu
Other KVM management tools
Virt-manager@wiki, GNOME_Boxes@wiki and OVirt@wiki are GUI versions of virtsh. See tools@kvm.
Rui's Blog 