Managing Xen on CentOS using the xm and virsh Command-line Tools
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In previous chapters we have covered the steps necessary to install and configure Xen and Xen based guest operating systems. This chapter is dedicated to explaining the xm and virsh tools, and how they may be used to manage Xen based guest operating systems running on CentOS from the command-line.
xm Command-line vs virsh Shell
Many of the tasks covered in this chapter can be performed using either the xm or virsh though in some cases the actual wording of the option may differ slightly. The primary difference is that the virsh command can be run in shell mode in addition to being used as a command line tool.
To use the options as command-line arguments, use them at a Terminal command prompt as shown in the following example:
su - xm list
A similar result can be achieved using virsh as a command-line tool:
virsh list
To run commands in the virsh shell, run the following command:
[root@centos5 ~]# virsh
Welcome to virsh, the virtualization interactive terminal.
Type: 'help' for help with commands
'quit' to quit
virsh #
At the virsh> prompt enter the options you wish to run, for example the following virsh session lists the current virtual machines, starts a virtual machine named MyXenVM and then obtains another listing to verify the VM is running:
su –
[root@centos5 ~]# virsh
Welcome to virsh, the virtualization interactive terminal.
Type: 'help' for help with commands
'quit' to quit
virsh # list
Id Name State
----------------------------------
0 Domain-0 running
virsh # start MyXenVM
Domain MyXenVM started
virsh # list
Id Name State
----------------------------------
0 Domain-0 running
3 MyXenVM idle
In the remainder of this chapter we will focus on using the xm command as opposed to the virsh command. This is simply to avoid duplication since many options used with xm can also be used with virsh. In the event that an option has a different name the equivalent virsh option can be found using the help keyword.
virsh help
Commands:
help print help
attach-device attach device from an XML file
attach-disk attach disk device
attach-interface attach network interface
autostart autostart a domain
capabilities capabilities
connect (re)connect to hypervisor
console connect to the guest console
create create a domain from an XML file
start start a (previously defined) inactive domain
destroy destroy a domain
detach-device detach device from an XML file
detach-disk detach disk device
detach-interface detach network interface
define define (but don't start) a domain from an XML file
domid convert a domain name or UUID to domain id
domuuid convert a domain name or id to domain UUID
dominfo domain information
domname convert a domain id or UUID to domain name
domstate domain state
domblkstat get device block stats for a domain
domifstat get network interface stats for a domain
dumpxml domain information in XML
edit edit XML configuration for a domain
find-storage-pool-sources discover potential storage pool sources
find-storage-pool-sources-as find potential storage pool sources
freecell NUMA free memory
hostname print the hypervisor hostname
list list domains
migrate migrate domain to another host
net-autostart autostart a network
net-create create a network from an XML file
net-define define (but don't start) a network from an XML file
net-destroy destroy a network
net-dumpxml network information in XML
net-edit edit XML configuration for a network
net-list list networks
net-name convert a network UUID to network name
net-start start a (previously defined) inactive network
net-undefine undefine an inactive network
net-uuid convert a network name to network UUID
nodeinfo node information
nodedev-list enumerate devices on this host
nodedev-dumpxml node device details in XML
nodedev-dettach dettach node device its device driver
nodedev-reattach reattach node device its device driver
nodedev-reset reset node device
nodedev-create create a device defined by an XML file on the node
nodedev-destroy destroy a device on the node
pool-autostart autostart a pool
pool-build build a pool
pool-create create a pool from an XML file
pool-create-as create a pool from a set of args
pool-define define (but don't start) a pool from an XML file
pool-define-as define a pool from a set of args
pool-destroy destroy a pool
pool-delete delete a pool
pool-dumpxml pool information in XML
pool-edit edit XML configuration for a storage pool
pool-info storage pool information
pool-list list pools
pool-name convert a pool UUID to pool name
pool-refresh refresh a pool
pool-start start a (previously defined) inactive pool
pool-undefine undefine an inactive pool
pool-uuid convert a pool name to pool UUID
quit quit this interactive terminal
reboot reboot a domain
restore restore a domain from a saved state in a file
resume resume a domain
save save a domain state to a file
schedinfo show/set scheduler parameters
dump dump the core of a domain to a file for analysis
shutdown gracefully shutdown a domain
setmem change memory allocation
setmaxmem change maximum memory limit
setvcpus change number of virtual CPUs
suspend suspend a domain
ttyconsole tty console
undefine undefine an inactive domain
uri print the hypervisor canonical URI
vol-create create a vol from an XML file
vol-create-as create a volume from a set of args
vol-delete delete a vol
vol-dumpxml vol information in XML
vol-info storage vol information
vol-list list vols
vol-path convert a vol UUID to vol path
vol-name convert a vol UUID to vol name
vol-key convert a vol UUID to vol key
vcpuinfo domain vcpu information
vcpupin control domain vcpu affinity
version show version
vncdisplay vnc display
Listing Guest System Status
The status of the host and guest systems may be viewed at any time using the list option of the xm tool. For example:
su - xm list
The above command will display output containing a line for the host system and a line for each guest similar to the following:
Name ID Mem VCPUs State Time(s) Domain-0 0 389 1 r----- 1414.9 MyXenVM 305 1 349.9 WindowsVM 300 1 0.0
The State column uses a single character to specify the current state of the corresponding guest.
These are as follows:
- r - running - The domain is currently running and healthy
- b - blocked - The domain is blocked, and not running or runnable. This can be caused because the domain is waiting on I/O (a traditional wait state) or has gone to sleep because there was nothing else for it to do.
- p - paused - The domain has been paused, typically as a result of the administrator running the xm pause command. When in a paused state 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, and the domain is in the process of being destroyed in response.
- c - crashed - The domain has crashed. Usually this state can only occur 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.
Starting a Xen Guest System
A guest operating system can be started using the xm tool combined with the start option followed by the name of the guest operating system to be launched. For example:
su - xm start myGuestOS
Connecting to a Running Xen Guest System
Once the guest operating system has started, a connection to the guest may be established using either the vncviewer tool or the virt-manager console. To use virt-manager, select Applications -> System Tools -> Virtual Machine Manager, select the desired system and click Open. To connect using vncviewer to the default virtual machine, enter the following command in Terminal window:
vncviewer
When prompted for a server enter localhost:5900. A VNC window will subsequently appear containing the running guest system. If you have multiple virtual machines running, the VNC port of virtual machine may be identified using the virsh command:
virsh vncdisplay WindowsVM :4
In order to connect to the console for the WindowsVM, therefore, the following command could be used:
vncviewer :4
Shutting Down a Guest System
The shutdown option of the xm tool is used to shutdown a guest operating system:
xm shutdown guestName
where guestName is the name of the guest system, to be shutdown.
Note that the shutdown option allows the guest operating system to perform an orderly shutdown when it receives the shutdown instruction. To instantly stop a guest operating system the destroy option may be used (with all the attendant risks of filesystem damage and data loss): xm destroy myGuestOS
Pausing and Resuming a Guest System
A guest system can be paused and resumed using the xm tool's pause and restore options. For example, to pause a specific system named myXenGuest:
xm pause myXenGuest
Similarly, to resume the paused system:
xm resume myXenGuest
Note that a paused session will be lost if the host system is rebooted. Also, be aware that a paused system continues to reside in memory. To save a session such that it no longer takes up memory and can be restored to its exact state after a reboot, it is necessary to either suspend and resume or save and restore the guest.
Suspending and Resuming a Guest OS
A running guest operating system can be suspended and resumed using the xm utility. When suspended, the current status of the guest operating system is written to disk and removed from system memory. A suspended system may subsequently be restored at any time (including after a host system reboot):
To suspend a guest OS named myGuestOS:
xm suspend myGuestOS
To restore a suspended guest OS:
xm resume myGuestOS
Saving and Restoring Xen Guest Systems
Saving and restoring of a Xen guest operating system is similar to suspending with the exception that the file used to contain the suspended operating system memory image can be specified by the user:
To save a guest:
xm save myGuestOS path_to_save_file
To restore a saved guest operating system session:
xm restore path_to_save_file
Rebooting a Guest System
To reboot a guest operating system:
xm reboot myGuestOS
Configuring the Memory Assigned to a Xen Guest OS
To configure the memory assigned to a guest OS, use the mem-set option of the xm command (the equivalent option for virsh is setmem). For example, the following command reduces the memory allocated to a guest system named myGuestOS to 256Mb:
xm mem-set myGuestOS 256
Note that acceptable memory settings must fall within the memory available to the current Domain. This may be increased using the mem-max option to xm.
Migrating a Domain to a Different Host
The migrate option allows a Xen managed domain to be migrated to a different physical server. In order to use migrate, Xend must already be running on the target host machine, and must be running the same version of Xen as the local host system. In addition, the remote host system must have the migration TCP port open and accepting connections from the source host. Finally, there must be sufficient resources for the domain to run (memory, disk space, etc).
xm migrate domainName host
Optional flags available with this command are:
-l, --live Use live migration.
-p=portnum, --port=portnum
Use specified port for migration.
-r=MBIT, --resource=MBIT
Set level of resource usage for migration.
For more information on performing Xen based live migrations, review Virtuatopia.com’s Migrating Xen domainU Guests Between Host Systems tutorial.
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You are reading a sample chapter from the CentOS 5 Essentials Essentials book. Purchase a copy of the fully updated CentOS 8 edition in eBook ($24.99) or Print ($36.99) format CentOS 8 Essentials Print and eBook (ePub/PDF/Kindle) editions contain 31 chapters and over 260 pages. Learn more...
|
| Previous | Table of Contents | Next |
| Configuring a New CentOS Xen Virtual Network | Installing KVM Virtualization on CentOS |
