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4.2. Demonstration: Creating and Managing a Guest with Command-line Utilities

To show how virtualization tasks are performed in the CLI, this section provides a demonstration where a new guest virtual machine is created, an OS is installed on it, and the guest is afterwards interacted with and managed using CLI commands.

4.2.1. Installation
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The following creates a new guest, here named guest1-rhel7, and starts an OS installation from a Red Hat Enterprise Linux 7 Workstation ISO image. This image is obtainable on the Customer Portal and in this example, it is currently located in your ~/Downloads/ folder. The guest is allocated with two virtual CPUs, 2048 MB RAM, and 8 GB of disk space. 
# virt-install --name guest1-rhel7 --memory 2048 --vcpus 2 --disk size=8 --cdrom /home/username/Downloads/rhel-workstation-7.4-x86_64-dvd.iso --os-variant rhel7

Starting install...
Allocating 'guest1-rhel7.qcow2'                                                   | 8.0 GB  00:00:00
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This launches a graphical Anaconda installer in the virt-viewer application. For more information on the installation, see the Installation Guide.
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Note

On host systems without access to a graphical interface, it is possible to install the guest OS using text-based Anaconda, using a virt-install command similar to the following: 
# virt-install -name rhel7anaconda-guest -r 1024 --location=/home/jherrman/Downloads/rhel-workstation-7.4-x86_64-dvd.iso --disk size=8 --nographics --extra-args="console=tty0 console=ttyS0,115200n8"
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If the installation completes successfully, the command line displays the following: 
Domain creation completed.
Restarting guest.
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It is now possible to make any desirable configuration to the guest. However, to manage the guest settings safely, it is advisable to shut down the guest first. 
# virsh shutdown guest1-rhel7
Domain guest1-rhel7 is being shutdown
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4.2.2. Attaching a Device
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To make the guest detect and use a USB device connected to the host, a Samsung mobile phone in this example, start by using the lsusb command on the host to retrieve the device's IDs. 
# lsusb

[...]
Bus 003 Device 007: ID 04e8:6860 Samsung Electronics Co., Ltd Galaxy (MTP)
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Afterwards, use your text editor of choice on the host to create an XML file for the device, samsung_USB_device.xml in this example, where you will input the vendor and product IDs. 
# vim samsung_USB_device.xml
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<hostdev mode='subsystem' type='usb' managed='yes'>
  <source>
    <vendor id='0x04e8'/>
    <product id='0x6860'/>
  </source>
</hostdev>
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Finally, use the virsh attach-device command to attach the device to the guest. 
# virsh attach-device guest1-rhel7 --file samsung_USB_device.xml --config
Device attached successfully
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Note

It is possible to attach devices to a running guest as well. To do so, use the --live option.

4.2.3. Interacting with the Guest
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To begin using the guest1-rhel7 guest, start it first. 
# virsh start guest1-rhel7
Domain guest1-rhel7 started
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Depending on whether your host system has a graphical display, you can either interact with the guest using the virt-viewer application, or using an SSH shell.
  • On systems with a graphical display, use virt-viewer: 
    # virt-viewer guest1-rhel7
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    Afterwards, you can interact with the screen output in the virt-viewer window like with an OS GUI on a physical machine. For example, you can use the Subscription Manager application to register your Red Hat Enterprise Linux guest OS:
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  • If the host or guest has a text-only interface, use SSH. This requires knowing the IP address of the guest. If you do not know the IP address, it can be obtained using the virsh domifaddr command. 
    # virsh domifaddr guest1-rhel7
 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:00:65:29:21    ipv4         10.34.3.125/24
# ssh root@10.34.3.125
root@10.34.3.125's password:
Last login: Wed Jul 19 18:27:10 2017 from 192.168.122.1
[root@localhost ~]#
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    Note

    For virsh domifaddr to work, the guest must be running, reachable on a network, and may require the QEMU guest agent to be activated.
    Afterwards, you can interact with the host terminal as if using a terminal on the guest machine. For example, you can use the subscription-manager utility to register your Red Hat Enterprise Linux guest OS: 
    [root@localhost ~]# subscription-manager register
Registering to: subscription.rhsm.redhat.com:443/subscription
Username: username@sample.com
Password:
The system has been registered with ID: 30b5e666-67f9-53bb-4b90-c2a88e5be789
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4.2.4. Diagnostics
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Display general information about the state of the guest: 
# virsh dominfo guest1-rhel7
Id:             1
Name:           guest1-rhel7
UUID:           ec0c0122-fb63-4a54-b602-5cf84f5e2dfd
OS Type:        hvm
State:          running
CPU(s):         2
CPU time:       33.4s
Max memory:     2097152 KiB
Used memory:    2097152 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: selinux
Security DOI:   0
Security label: unconfined_u:unconfined_r:svirt_t:s0:c102,c792 (enforcing)
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4.2.5. Creating Snapshots
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To back up the state of the guest, you can use the virsh snapshot-create command. 
# virsh snapshot-create guest1-rhel7
Domain snapshot 1500563241 created
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You can display your current snapshots and the XML setting of each one. 
# virsh snapshot-list guest1-rhel7
Name                 Creation Time             State
------------------------------------------------------------
1500563241           2017-07-20 17:07:21 +0200 shutoff

# virsh snapshot-dumpxml guest1-rhel7 1500563241
<domainsnapshot>
  <name>1500563241</name>
  <state>shutoff</state>
  <creationTime>1500563241</creationTime>
  <memory snapshot='no'/>
  <disks>
    <disk name='vda' snapshot='internal'/>
[...]
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This snapshot can later be loaded to revert the guest to the state saved in the snapshot. 
# virsh snapshot-revert guest1-rhel7 --snapshotname 150056324
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