Virtualization cheat sheet

Posted by Amol Dighe on July 22, 2017
  • Create a disk image for virtual machine
qemu-img create -f qcow2 /home/amol/Documents/ISO/oraclelinu66-2.qcow2 6G

Formatting '/home/amol/Documents/ISO/oraclelinu66-2.qcow2', fmt=qcow2 size=6442450944 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
  • Create a domain and spawn a virtual machine
virt-install --name oracle66-2 --vcpus=1 --ram=2048 --disk path=/home/amol/Documents/ISO/oraclelinu66-2.qcow2,bus=virtio,cache=writeback --graphics vnc,listen= --network bridge:virbr0,model=virtio --noautoconsole --os-type=linux --os-variant=rhel6 --location=/home/amol/Documents/ISO/OracleLinux66_V52218-01.iso

Starting install...
Retrieving file .treeinfo...                                                                                                   | 1.5 kB  00:00:00     
Retrieving file vmlinuz...                                                                                                     | 4.0 MB  00:00:00     
Retrieving file initrd.img...                                                                                                  |  34 MB  00:00:00     
Creating domain...                                                                                                             |    0 B  00:00:01     
Domain installation still in progress. You can reconnect to 
the console to complete the installation process.
  • Modify file content inside a Virtual Machine using guestfish
guestfish --rw -a /tmp/OracleLinux-66.img -i edit /etc/ssh/sshd_config
  • Remove a package from qcow2 image, without booting into the Virtual Machine
guestfish --rw -a /tmp/OracleLinux-66.img -i command "yum remove cloud-init -y"

Loaded plugins: security
Setting up Remove Process
Resolving Dependencies
--> Running transaction check
---> Package cloud-init.noarch 0:0.7.4-2.el6 will be erased
--> Finished Dependency Resolution

Dependencies Resolved

 Package             Arch            Version               Repository      Size
 cloud-init          noarch          0.7.4-2.el6           @epel          1.7 M

Transaction Summary
Remove        1 Package(s)

Installed size: 1.7 M
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Erasing    : cloud-init-0.7.4-2.el6.noarch                                1/1
  Verifying  : cloud-init-0.7.4-2.el6.noarch                                1/1

  cloud-init.noarch 0:0.7.4-2.el6

  • Modify user password for a VM using guestfish
guestfish --rw -a /tmp/OracleLinux-66.img -i command "bash -c 'echo admin:amol123 | chpasswd'"
  • Attach a new interface to an existing virtual machine
virsh attach-interface --domain oracle66-2 --type bridge --source br-new --model virtio

This will attach an additional bridge interface to the VM and same will be visible as a new interface inside the VM.

  • Logs location for openstack VM

Openstack would crreate a VM log file at the below path with id of the VM


qemu will create a log file at the below path with id of the instance


The instance & openstack VM id can be grep from the qemu process

root@cpu-node:~# ps -ef | grep instance-000039c8

root     50890 32187  0 19:50 pts/3    00:00:00 grep --color=auto instance-000039c8

libvirt+ 64262     1  2 Jun01 ?        13:03:17 qemu-system-x86_64 -enable-kvm -name instance-000039c8 -S -machine pc-i440fx-trusty,accel=kvm,usb=off -cpu host -m 65536 -realtime mlock=off -smp 16,sockets=16,cores=1,threads=1 -uuid 1212b55f-5a62-406a-89ca-706c03657251 -smbios type=1,manufacturer=OpenStack Foundation,product=OpenStack Nova,version=12.0.4,serial=34383137-3630-4753-4835-3531584c3753,uuid=1212b55f-5a62-406a-89ca-706c03657251,family=Virtual Machine -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/instance-000039c8.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=discard -no-hpet -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=rbd:volumes/volume-afa54dd1-dd47-40a5-acd6-5ff4d653277e:id=volumes:key=AQDgMEFY27UcERAAX4p8GvgdTytz0i/aoMK7JA==:auth_supported=cephx\;none:mon_host=\:6789\;\:6789\;\:6789,if=none,id=drive-virtio-disk0,format=raw,serial=afa54dd1-dd47-40a5-acd6-5ff4d653277e,cache=writeback -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -drive file=rbd:volumes/volume-55d25150-3c43-49e3-ac44-d3b64ee53320:id=volumes:key=AQDgMEFY27UcERAAX4p8GvgdTytz0i/aoMK7JA==:auth_supported=cephx\;none:mon_host=\:6789\;\:6789\;\:6789,if=none,id=drive-virtio-disk1,format=raw,serial=55d25150-3c43-49e3-ac44-d3b64ee53320,cache=writeback -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk1,id=virtio-disk1 -netdev tap,ifname=tapa42f54ba-91,script=,id=hostnet0,vhost=on,vhostfd=27 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=02:a4:2f:54:ba:91,bus=pci.0,addr=0x3 -chardev file,id=charserial0,path=/var/lib/nova/instances/1212b55f-5a62-406a-89ca-706c03657251/console.log -device isa-serial,chardev=charserial0,id=serial0 -chardev pty,id=charserial1 -device isa-serial,chardev=charserial1,id=serial1 -device usb-tablet,id=input0 -vnc -k en-us -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -msg timestamp=on
  • Tools for playing with qemu-kvm disk image, disk partitions, filesystem

There are virt & qemu tools available to tweak disk images :



While disk partition can be altered with :


Next is the filesystem which can be resized using :


Tuning filesystem parameters:


Mounting VM disk image:


  • Command for KVM - Guest / Virtual Machine stat check

List VM and fetch its hardware status information

root@hp-envy:/mnt/srcVM# virsh list 
 Id    Name                           State
 1     ubuntu14                       running

root@hp-envy:/mnt/srcVM# virsh dominfo ubuntu14
Id:             1
Name:           ubuntu14
UUID:           f55e0174-6e75-4ed8-a09c-705cacfe8653
OS Type:        hvm
State:          running
CPU(s):         1
CPU time:       8.9s
Max memory:     1048576 KiB
Used memory:    1048576 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: apparmor
Security DOI:   0
Security label: libvirt-f55e0174-6e75-4ed8-a09c-705cacfe8653 (enforcing)

Get VM CPU details:

root@hp-envy:~# virsh domstats --vcpu ubuntu14
Domain: 'ubuntu14'

"vcpu.current" - current number of online virtual CPUs
"vcpu.maximum" - maximum number of online virtual CPUs
"vcpu.<num>.state" - state of the virtual CPU <num>
"vcpu.<num>.time" - virtual cpu time spent by virtual CPU <num> (in microseconds)
"vcpu.<num>.wait" - virtual cpu time spent by virtual CPU <num> waiting on I/O (in microseconds)
"vcpu.<num>.halted" - virtual CPU <num> is halted: yes or no 
root@hp-envy:~# virsh domstats --cpu-total ubuntu14
Domain: 'ubuntu14'

"cpu.time" - total cpu time spent for this domain in nanoseconds
"cpu.user" - user cpu time spent in nanoseconds
"cpu.system" - system cpu time spent in nanoseconds

VM memory stats

root@hp-envy:~# virsh dommemstat  ubuntu14
actual 1048576
swap_in 0
last_update 1514374267
rss 288460

swap_in           - The amount of data read from swap space (in kB)
actual            - Current balloon value (in KB)
rss               - Resident Set Size of the running domain's process (in kB)
last-update       - Timestamp of the last update of statistics (in seconds)

Print a table showing the brief information of all block devices associated with domain.

root@hp-envy:~# virsh domblklist  ubuntu14
Target     Source
vda        /var/lib/libvirt/images/ubuntu-server-1404.img
hda        /var/lib/libvirt/images/config-node.iso

Get block device size info for a domain.

root@hp-envy:~# virsh domblkinfo  ubuntu14 vda --human
Capacity:       2.199 GiB
Allocation:     393.324 MiB
Physical:       393.375 MiB

root@hp-envy:~# virsh domblkinfo  ubuntu14 hda --human
Capacity:       364.000 KiB
Allocation:     364.000 KiB
Physical:       364.000 KiB

VM block device stats.

root@hp-envy:~# virsh domblkstat  ubuntu14 --human
 number of read operations:      4735
 number of bytes read:           104040094
 number of write operations:     245
 number of bytes written:        4592640
 number of flush operations:     28
 total duration of reads (ns):   38175594855
 total duration of writes (ns):  1831031913
 total duration of flushes (ns): 5564971530

List interface used for the Virtual Machine

root@hp-envy:~# virsh domiflist ubuntu14
Interface  Type       Source     Model       MAC
vnet0      bridge     virbr0     virtio      52:54:00:e4:53:22

List the Virtual Machine data transfer details.

root@hp-envy:~# virsh domifstat ubuntu14 vnet0
vnet0 rx_bytes 142202
vnet0 rx_packets 2626
vnet0 rx_errs 0
vnet0 rx_drop 0
vnet0 tx_bytes 6300
vnet0 tx_packets 59
vnet0 tx_errs 0
vnet0 tx_drop 0

List the active network

root@hp-envy:~# virsh net-list
 Name                 State      Autostart     Persistent
 default              active     yes           yes

Get a list of dhcp leases for all network interfaces connected to the given virtual network

root@hp-envy:~# virsh net-dhcp-leases default 
 Expiry Time          MAC address        Protocol  IP address                Hostname        Client ID or DUID
 2017-12-27 20:15:35  52:54:00:e4:53:22  ipv4        cfg01           -