Revision as of 10:13, 18 April 2017

Chapter 4: Using Xen Project

Configuring and Booting Virtual Machines

Welcome to chapter 4, I bet this chapter is, the more interested chapter for you and you can learn to run and manage your Virtual Machines via The Xen Project. In this chapter, we show you how you can configure DomU and setting up your network and storage. We knows, You are familiar with Linux but we show you some Linux tools for manage LVM and create your partitions. After this chapter, You can manage Xen Project and your Virtual Machines and Install GNU/Linux and Windows OS on your Xen Project ax DomU. We will speak about a tool with the name “ virt-manager” that is a Graphical tool for managing your Vms.

By default, Fedora Server edition not have any Graphical Environment and as you know, The Graphical Environment need a lot of resources and not a good idea for server. So, System administrator don't like to install Graphical Environment and prefer CLI. You may ask yourself, Some Graphical Environment like “XFCE” need low resources but compared with CLI they need more resources.

Manage virtual machines with virt-manager

We want to show you “virt-manager” and it is a graphical program, Thus we need to install a Graphical Environment. Popular Desktops in Fedora are “Gnome” , “KDE” , “XFCE” and “MATE” but you can use other Desktops too.

For Install a Graphical Environment use below commands :

Gnome :

# yum groupinstall gnome

or

# yum groupinstall gdm

KDE :

# yum groupinstall kde

XFCE :

# yum groupinstall xfce

MATE :

# yum groupinstall "MATE Desktop”

When installing finished just run below command :

# startx

And after it you can see your Desktop. Mine is:

Figure 18 : MATE Desktop.

Open a “Terminal” and type below command for installing “Virt-Manager” :

# yum install virt-manager

After it you can run “virt-manager”.

Usually, Xen Masters use LVM volumes to store the Xen guest virtual disks and we will explain it in the future and skip it now, But just know that you can use Virtual HDD and real partition for your Guest DomU.

The Virt-manager, provide a good GUI and you can create your DomU via it very easy :

Figure 19 : Virt-Manager (OpenSUSE).

Figure 20 : Virt-Manager (Create Fedora 22 as DomU on OpenSUSE).

As you see, It is easy as ABC and give you this ability to run your own DomU guest via a nice Graphical interface.

Note that, If after install Graphical Environment your Xen Project show you an error, Then don't worry and Just Reinstall the Xen Project via below command :

# dnf reinstall xen*

After, Everything back to a right point.

If you start “Virt-Manager” and see some error like “unable to connect to libvirt” then don't worry, Just type below command :

# service libvirtd restart

You as a Linux administrator know that Linux has “/var/log/” directory that record everything that happening in your system. After install Xen, The Xen Project create a directory with the name “xen” under “/var/log” and all Xen errors and...recorded under this directory. If you encounter with any error just see “/var/log/xen/”.

OK, It is enough and you are familiar with “Virt-Manager”. Now, It is a good time for speaking about “ Storage and Networking”. Let's Go!

Storage and Networking

The Xen Project can use your real partition on your HDD as a Guest HDD and you can add HDD image also. We say it “Local Storage”. The Local Storage can partitioned via a tool like “LVM” or you can save your HDD image as a file on it. Let me to speak about LVM more.

LVM or Logical Volume Manager is a device mapper in Linux. You may ask, What is Device Mapper? OK, The Device Mapper is a framework that provided by The Linux Kernel and its goal is mapping physical block devices onto high-level virtual block devices. Device Mapper passing data from a virtual block device to another block device. The LVM provide logical volume management for the Linux Kernel and a method of allocating space on storage devices. LVM is more flexible that traditional partitioning. When you install Linux, It selected a best method for partitioning by default.

You can consider “LVM” as a "dynamic partitions", Its mean that you can create/resize/delete partitions while your Linux is running and you don't need any reboot for influence. LVM have many benefits but some of important of them are :

It can support more than one HDD.

LVM can be created to support RAID. including RAID 1, RAID 5 and RAID 6

It can support HA (High availability) and is a good option for Clusters.

Save space. Small chunks of unused space from several disks can be combined to create a usable volume.

With a lot of features, It has some bad things too. For example, the initial set-up of LVM is more complex than just partitioning a disk and you must understand LVM scheme and models.

It a good figure that help you to understand LVM easily :

Figure 21 : LVM Scheme.

I guess you understand it better. I want to show you some Linux Tools that via them you can manage your HDDs.

The first tool that we cover here is “fdisk” or “cfdisk”. Just type :

# cfdisk

or

# fdisk -l

I bet you will found “cfdisk” more friendly. The “fdisk -l” command will show you all of your partitions and HDD on your system. For example, For mine is :

[root@localhost ~]# fdisk -l

Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: dos

Disk identifier: 0xed8a6a75

Device Boot Start End Sectors Size Id Type

/dev/sda1 2048 662710271 662708224 316G 8e Linux LVM

Disk /dev/mapper/fedora-root00: 300 GiB, 322122547200 bytes, 629145600 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/fedora-swap: 16 GiB, 17179869184 bytes, 33554432 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

And “cfdisk” :

Figure 22 : cfdisk.

OK. The first method that we choice is using your real partition as guest HDD.

I added a new HDD to my system and linux detected it as “sdb”. Let me to tell you how Linux detect Device/Drive names. If you look at “/dev/” directory then you will find interesting names. Linux detect IDE Disk as “hd” and SCSI disks as “sd”. The complete scheme is “/dev/xxyn”. The “xx” is “hd” or “sd” as we said and :

Y : It is a letter that indicate the number of Hard Disk. For example, “hda” mean the first IDE disk and “sda” mean the first SCSI Disk.

N : It is a number that indicate the number of partition. Don't forget, The first four partitions (primary or extended) are in range 1..4. Logical partitions start from 5. For example, “/dev/hda2” mean the first IDE Hard Disk and The second primary or extended partition and “/dev/sdb5” mean the first logical partition on second SCSI hard disk.

We explained it because we don't like you remove other partitions and lost your data.

I added a new HDD to my system and Linus detected it as “sdb”. I use below command for look at my new HDD :

# cfdisk /dev/sdb

Figure 23 : cfdisk.

Create a partition via “cfdisk” is straightforward and don't need any teach, But don't forget to select “Empty” as your file system. Our suggestion is that don't create any partition and just use “parted” tool as below.

I used a tool with the name “parted” as below :

# parted /dev/sdb mklabel msdos

It show you a warning message about that all of your information will be destroy. Type “yes” and enter. Then, Write below command :

# parted /dev/sdb mkpart primary

after this command, Linux ask you some questions, I selected default file system (ext2) and enter “1” as “Start” and “100%” as “End”.

What do you see? Linux created a partition for you with the name “/dev/sdb1”. You can confirm it via below command :

# fdisk /dev/sdb -l

Figure 24 : fdisk.

After it, I want enable “LVM” for this partition and use below command :

# parted -s /dev/sdb set 1 lvm on

In above command I used “set 1” that mean partition 1. Let me to see our partitions via “fdisk” command :

# fdisk /dev/sdb -l

Figure 25 : fdisk -l.

Look carefully, You can see “LVM” at the end of line. It mean that “LVM” enable for our partition.

Type below command :

# pvcreate /dev/sdb1

# vgcreate Xen /dev/sdb1 -v

Figure 26 : vgcreate.

# lvcreate -L 8G -v -n Fedora Xen

In above command, You should select your size (We selected 8 Gigabyte) and logical volume name (Fedora) and a name that you typed in the previous command (Xen). The output is :

Figure 27 : lvcreate.

Let me to see our LVM via “vgdisplay” command :

# vgdisplay | more

Figure 28 : vgdisplay-1.

Figure 29 : vgdisplay-2.

OK, our storage is ready and we just need to create a config file for our VM. Before we dive into config file, Please let us for write something about “Networking”.

Networking in Xen

Create and configure network in real world is a hard job and can be complex in some areas. In VM world it can be complex too and depending on the network diagram. We never explain networking here complete byt we just show you how you can configure a simple network for your VM and your VM able to see external world.

It is true that Virtual Machines share your interfaces but it is not true that you must not concern about the security.

The Xen Project support some kind of networking that we will show you them here :

Bridge : Dom0 and DomU are connected to each other via a virtual network. It is a default and most common configuration. In this configuration, a software bridge created in the backend domain and the Virtual network connected to your physical network. For bridging you can use two schemes :1) Linux detect your NIC as “eth0” and in the first scheme, Your eth0 renamed to other name (myeth0) and bridge changed to eth0 2) in the second scheme, Your NIC remain eth0 and your bridge is mybr0.

Names are personalisation and you can select other names.

NAT : Network Address Translation or NAT is kind of routing and each guest have its own IP address. In NAT, Dom0 configured to forward your packets and iptables used to configure your Dom0 Kernel as a IP packet filter. NAT using RFC1918 addresses (http://tools.ietf.org/html/rfc1918).

Routing : In Routing your Dom0 configured for forward packets and a point-to-point link created between Dom0 and each DomU Virtual NIC. Don't forget, because of nature of routing, each of guest NIC must have static IP address.

OK, Xen need bridge for running and we want to show that you how you can create a Bridge for The Xen Project.

Depend on your Linux Distro (Dom0) you can use some tools for create a bridge in easy way. For example, On Fedora and Debian you can use “bridge-utils” for configure your Bridge.

My Current config are :

enp7s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500

inet 172.30.9.20 netmask 255.255.255.0 broadcast 172.30.9.255

inet6 fe80::52e5:49ff:fe40:c48f prefixlen 64 scopeid 0x20<link>

ether 50:e5:49:40:c4:8f txqueuelen 1000 (Ethernet)

RX packets 989 bytes 84310 (82.3 KiB)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 77 bytes 9575 (9.3 KiB)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536

inet 127.0.0.1 netmask 255.0.0.0

inet6 ::1 prefixlen 128 scopeid 0x10<host>

loop txqueuelen 1 (Local Loopback)

RX packets 83 bytes 9332 (9.1 KiB)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 83 bytes 9332 (9.1 KiB)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500

inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255

ether 52:54:00:8b:c5:55 txqueuelen 1000 (Ethernet)

RX packets 0 bytes 0 (0.0 B)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 0 bytes 0 (0.0 B)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

As you see, Fedora detect my NIC as “enp7s0” and its IP address is “172.30.9.20”. I must tell you that it is a static IP and not DHCP. I will tell you something about DHCP too.

I want to create a bridge that use this static IP, So I create a file via below command :

# touch /etc/sysconfig/network-scripts/ifcfg-br0

Then open it via an editor like “nano” and fill it with below information :

DEVICE=br0

TYPE=Bridge

BOOTPROTO=none

ONBOOT=yes

IPADDR=172.30.9.20

PREFIX=24

GATEWAY=172.30.9.254

DNS1=172.30.9.1

DELAY=0

NM_CONTROLLED=no

But, If your real NIC use DHCP protocol then you should use below config for Bridge :

DEVICE=br0

TYPE=Bridge

BOOTPROTO=dhcp

ONBOOT=yes

DELAY=0

NM_CONTROLLED=no

After it, I must change my real NIC configuration, So I open it via an editor :

# nano /etc/sysconfig/network-scripts/ifcfg-enp7s0

HWADDR=50:E5:49:40:C4:8F

TYPE=Ethernet

BOOTPROTO=none

DEFROUTE=yes

IPV4_FAILURE_FATAL=no

IPV6INIT=yes

IPV6_AUTOCONF=yes

IPV6_DEFROUTE=yes

IPV6_FAILURE_FATAL=no

NAME=enp7s0

UUID=5e520f04-b32c-4116-b61f-89c190868edc

ONBOOT=yes

#IPADDR=172.30.9.20

#PREFIX=24

#GATEWAY=172.30.9.254

#DNS1=172.30.9.1

IPV6_PEERDNS=yes

IPV6_PEERROUTES=yes

IPV6_PRIVACY=no

NM_CONTROLLED=no

BRIDGE=br0

As you see, My current NIC configuration use “BOOTPROTO=none” and its mean Static IP and if it was “DHCP” then you can't see any parts like “IPADDR”, “ PREFIX”, “GATEWAY” and “ DNS1” because all of these parts gaining automatically. Because of I added all of these parts to my Bridge then I must remove these parts from real NIC configuration file and add “NM_CONTROLLED=no” and “BRIDGE=br0” at the end of file. Don't forget, “br0” is my bridge name and you can select any name that you like.

If my NIC use DHCP protocol then I didn't need any extra works.

Everything is ready and I must restart my network service for take affect :

# systemctl restart network.service

After it, you can see current configuration via “ifconfig” command as below :

br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500

inet 172.30.9.20 netmask 255.255.255.0 broadcast 172.30.9.255

inet6 fe80::52e5:49ff:fe40:c48f prefixlen 64 scopeid 0x20<link>

ether 50:e5:49:40:c4:8f txqueuelen 1000 (Ethernet)

RX packets 846 bytes 62175 (60.7 KiB)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 129 bytes 11550 (11.2 KiB)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

enp7s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500

inet6 fe80::52e5:49ff:fe40:c48f prefixlen 64 scopeid 0x20<link>

ether 50:e5:49:40:c4:8f txqueuelen 1000 (Ethernet)

RX packets 5479 bytes 468651 (457.6 KiB)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 558 bytes 75815 (74.0 KiB)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536

inet 127.0.0.1 netmask 255.0.0.0

inet6 ::1 prefixlen 128 scopeid 0x10<host>

loop txqueuelen 1 (Local Loopback)

RX packets 83 bytes 9332 (9.1 KiB)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 83 bytes 9332 (9.1 KiB)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500

inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255

ether 52:54:00:8b:c5:55 txqueuelen 1000 (Ethernet)

RX packets 0 bytes 0 (0.0 B)

RX errors 0 dropped 0 overruns 0 frame 0

TX packets 0 bytes 0 (0.0 B)

TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

As you see, A Bridge with the name “br0” created and all information of my real NIC (enp7s0) given to my bridge. So, my Bridge work like my real NIC. Don't forget for each Physical NIC you should create a Bridge.

Our network is ready and we must create a Guest config.

Installing Windows as HVM domainU Guest

Huh, Are you ready? It is the most exciting part of our book and we to show you how you can install your Guest OS.

We choice Window 7 Enterprise for install as Guest and show you that how you can configure your Xen to use this “.iso” file and start your VM.

First of all, We must create a config file for our VM. Let me to create it via “touch” command in Linux :

# touch /etc/xen/windows.cfg

Then, I open it via an editor like “nano” as below :

# nano /etc/xen/windows.cfg

And fill this file via below information :

name = "Windows7"

builder = "hvm"

vcpus = 4

memory = "4096"

maxmex= "8192"

vif=['bridge=br0']

disk=['phy:/dev/Xen/Fedora,hda,w','file:/home/mohsen/windows7.iso,hdc:cdrom,r']

vnc="1"

vnclisten="172.30.9.20"

vncconsole="0"

boot="dc"

stdvga=1

videoram=32

on_poweroff = "destroy"

on_reboot = "restart"

on_crash = "restart"

I must tell you something about this file :

vif=['bridge=br0'] : Because of we choice “br0” as a name of our Bridge then we must write “'bridge=br0'” ,But if your Bridge name is different then you must write your Bridge name instead of it here.

disk=['phy:/dev/Xen/Fedora,hda,w','file:/home/mohsen/windows7.iso,hdc:cdrom,r'] : If you remember, We want to use our real partition as our Guest partition, Thus it is not a File that act as a real HDD. Because of it, We used “phy” that mean Physical. The “Xen” is our LVM and I choice “Fedora” as a name of my 20 GB partition on LVM. You may selected other name that you must put it here.

Vnclisten="172.30.9.20" : Because I use the Xen Project on other server and not on my current PC, I must define the IP address of my Xen Server. My Xen Server IP is “172.30.9.20” and if your situation is like us then you must write your Xen Server IP here but if you run the Xen Project on your PC and not another PC or Server then you must write “vnclisten="0.0.0.0"”. When you select “0.0.0.0” as IP then it is your local host.

boot="dc" : the “d” mean “CDROM” and “c” mean your HDD. It is your Boot order and when you Guest installed you can change it to “boot=”c””. The Xen Project parameters are boot on floppy (a), hard disk (c), Network (n) and CD-ROM (d).

Let us start our Guest. Just type below command :

# xl create /etc/xen/windows.cfg

and if you have not any error in your syntax then your xen just show “Parsing config from /etc/xen/windows.cfg” and your VM started.

After it write below command :

# xl list

and you can see something like below :

Name ID Mem VCPUsStateTime(s)

Domain-0 0 3659 8 r----- 887.6

Windows7 19 4096 4 -b---- 23.1

As you see, “Windows7” is running and we just need connect to it via “vncviewer”. But you must did something on your Firewall.

Linux use “iptables” as Firewall and VNC Port is not opened by default and we must open this port for connect to our VNC remotely. Don't forget, We doing it because our Xen server is on another PC and we must connect to it remotely thus we need open VNC Port. The VNC use Port 5900 and TCP protocol.

I use “netstat -nat” command for show our current network connections :

# netstat -nat

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 172.30.9.20:5900 0.0.0.0:* LISTEN

tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

tcp 0 0 172.30.9.20:22 172.30.10.18:49824 ESTABLISHED

tcp6 0 0 :::9090 :::* LISTEN

tcp6 0 0 :::22 :::* LISTEN

As you see, The IP “172.30.9.20” and Port “5900” are ready for connect but we must doing some steps for connect to our VM :

1- First of all, Install a tool like “vncviewer” on your Linux Distro.

2- Depend on your Linux Distro (Dom0) you must use “iptables” for open VNC Port on Dom0 :

# iptables -A INPUT -p tcp --dport 5900 -j ACCEPT

# iptables-save

After it, The Port “5900” is open on your Dom0 and you can connect to it remotely. You can use “iptables -L” for show your current iptables rules.

We ready ready to connect to our Xen Server :

# vncviewer 172.30.9.20:5900

And after it, A window displayed and we can do Windows install process:

Figure 30 : Windows 7 on Xen.

Sometimes you don't like your VM viewed by others and you want set password for it, For do it use below parameter in your VM config file :

vncpasswd=”Your Password”

After it, When you want view your VM via VNC you must enter a password :

vncviewer 172.30.9.20:5900

Connected to RFB server, using protocol version 3.8

Performing standard VNC authentication

Password:

When you working with Your VM, You may have some problems with your Display and you must consider below Links for Troubleshooting your problems :

http://wiki.xenproject.org/wiki/Xen_Common_Problems#How_do_I_change_the_resolution_of_Xen_PV_domU_vfb_graphical_VNC_console.3F

http://wiki.xenproject.org/wiki/Xen_Common_Problems#How_can_I_get_resolutions_larger_than_800x600_for_Xen_HVM_guest_graphical_VNC_console.3F

A good note that you must consider it is that you should install “Windows PV Drivers” for your Xen VM. Navigate to “http://www.xenproject.org/downloads/windows-pv-drivers.html” and download .TAR files and extract them, then configure your NIC IP address and see your network and copy these files and install them on your Windows Guest. In below figure you can see that I choice a static IP for my Windows Guest :

Figure 31 : Static IP.

When you create another VM:

[root@localhost ~]# netstat -nat

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 172.30.9.20:5900 0.0.0.0:* LISTEN

tcp 0 0 172.30.9.20:5901 0.0.0.0:* LISTEN

tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

tcp 0 0 172.30.9.20:5900 172.30.10.18:33869 ESTABLISHED

tcp 0 0 172.30.9.20:22 172.30.10.18:55000 ESTABLISHED

tcp 0 180 172.30.9.20:22 172.30.10.18:54616 ESTABLISHED

tcp6 0 0 :::9090 :::* LISTEN

tcp6 0 0 :::22 :::* LISTEN

[root@localhost ~]# xl list

Name ID Mem VCPUsStateTime(s)

Domain-0 0 1590 8 r----- 192.7

Windows7 9 4096 4 -b---- 21.0

linux 10 2048 1 r----- 64.8

If you pay attention to the output of “ifconfig” command then you will see a default Bridge with the name “virbr0”. We can use this Bridge for add other NIC to our VM. For example, We need more than one NIC on our VM.

For adding more than one NIC you can use :

vif=['bridge=br0','mac=00:16:17:a5:6y:89,bridge=virbr0']

The “mac” defined the MAC address for our NIC.

We can use our first Bridge(br0) for adding more than NIC too but we should add a MAC address fpr each NIC :

vif=['bridge=br0,mac=00:13:r6:45:g6:9o','mac=00:16:17:a5:6y:89,bridge=br0']

In above example, We used the Bridge br0 for adding two NICs but we can't create another Bridge(br1) and attach it other Physical NIC and use it here.

Share storage between VMS

In some situation, You may want to use another HDD or other Vms HDD in a VM. It is so easy and you can write the name of your other HDD in “disk” in the config file :

disk=['phy:/dev/Xen/Fedora,hda,w','phy:/dev/Xen/linux,hdb,w','file:/home/mohsen/Windows7.iso,hdc:cdrom,r']

In above example, my main HDD is “Fedora” and I mount another HDD (linux) as “hdb”. When I fire my “vm” then I can see other HDD in my vm. If you noted, Then you can see “w” and “r” word at the end of my lines. What are these? The “w” mean “read-write” and “r” mean “read-only”.

VM States in The Xen Project

When you run a VM through Xen and run “xl list” then you can see a column with the name “State” and a word that changed sometimes. What does this word mean?

For example, I run “xl list” and the output is as below :

[root@localhost ~]# xl list

Name ID Mem VCPUsStateTime(s)

Domain-0 0 1590 8 r----- 1211.3

OpenSUSE 44 2048 1 r----- 4.6

I will tel you something about these words :

r - running

The domain is currently running.

b - blocked

The domain is blocked, and not running or runnable. This happened when the domain is waiting on IO or going to sleep because there was nothing else for it to do.

p - paused

The domain has been paused, and may administrator paused it via “xl pause” command. When a VM paused, The domain will still consume allocated resources like memory, but will not be eligible for scheduling by the Xen hypervisor.

s - shutdown

The guest has requested to be shutdown, rebooted or suspended.

c - crashed

The domain has crashed. It may if the domain has been configured not to restart on crash.

d - dying

The domain is in process of dying, but hasn't completely shutdown or crashed.

In below example, my “OpenSUSE” VM is running and established :

[root@localhost ~]# xl list

Name ID Mem VCPUsStateTime(s)

Domain-0 0 1590 8 r----- 1245.3

OpenSUSE 44 2048 2 -b---- 127.4

Then, I run below command for “Pause” it :

# xl pause OpenSUSE

and my current state is:

[root@localhost ~]# xl list

Name ID Mem VCPUsStateTime(s)

Domain-0 0 1590 8 r----- 1248.0

OpenSUSE 44 2048 2 --p--- 127.5

For “unpause” a VM you can use below command :

# xl unpause OpenSUSE

[root@localhost ~]# xl list

Name ID Mem VCPUsStateTime(s)

Domain-0 0 1590 8 r----- 1257.0

OpenSUSE 44 2048 2 -b---- 128.3

Add USB Devices to your VM

Sometime you may want to add a USB device to your VM. Linux has a command with the name “lsudb” that show your USB controllers on your Server :

[root@localhost ~]# lsusb

Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub

Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Bus 006 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Bus 001 Device 003: ID 13ba:0017 PCPlay PS/2 Keyboard+Mouse Adapter

Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

As you see, My Server has USB 2.0 and USB 3,0 controllers. I plugged a HP Pendrive to my server and run command again :

[root@localhost ~]# lsusb

Bus 002 Device 003: ID 03f0:5607 Hewlett-Packard