Wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
==== Local libvirt access ====
=== Overview ===
The command line tool of choice for accessing the libvirt process is ''virsh''. The command ''virsh help'' shows all defined sub-commands. The sub-commands are organized in the following command groups: 
  root@kvm55:~# virsh help |grep 'help keyword'
   Domain Management (help keyword 'domain'):
   Domain Monitoring (help keyword 'monitor'):
   Host and Hypervisor (help keyword 'host'):
   Interface (help keyword 'interface'):
   Network Filter (help keyword 'filter'):
   Networking (help keyword 'network'):
   Node Device (help keyword 'nodedev'):
   Secret (help keyword 'secret'):
   Snapshot (help keyword 'snapshot'):
   Storage Pool (help keyword 'pool'):
   Storage Volume (help keyword 'volume'):
   Virsh itself (help keyword 'virsh'):
With the help of the keywords detailed help to commands of command groups can be derived:
  root@kvm55:~# virsh help secret
   Secret (help keyword 'secret'):
      secret-define            define or modify a secret from an XML file
      secret-dumpxml           secret attributes in XML
      secret-get-value         Output a secret value
      secret-list              list secrets
      secret-set-value         set a secret value
      secret-undefine          undefine a secret
The help content for a single sub-command can be displayed with the command ''virsh help <sub-command>'':      
  root@kvm55:~# virsh help define
    NAME
      define - define (but don't start) a domain from an XML file
  
    SYNOPSIS
      define <file>
  
    DESCRIPTION
      Define a domain.
  
    OPTIONS
      [--file] <string>  file containing an XML domain description
=== Command overview ===
The most important virsh sub-commands for everyday use are summarized in the following table.
^ No. ^ command ^ use ^
| 1 | virsh list | display host names of active virtual hosts |
| 2 | virsh list --all | display host names of all defined (active and not active) virtual hosts |
| 3 | virsh start <vhost> | start a virtual host |
| 4 | virsh shutdown <vhost> | shut down a running virtual host |
| 5 | virsh reboot <vhost> | reboot a running virtual host |
| 6 | virsh destroy <vhost> | shut off a running virtual host abruptly | 
| 7 | virsh suspend <vhost> | stop a running virtual host |
| 8 | virsh resume <vhost> | continue running a stopped virtual host |
| 9 | virsh save <vhost> <file> | save the memory of a virtual host into a file and stop the virtual host afterwards |
| 10 | virsh restore <file> | restore the memory of a virtual host from a file and continue running the virtual host |
| 11 | virsh dumpxml <vhost> | output the virtual host definition in XML format | 
| 12 | virsh define <file> | read the virtual host definition from a XML file |
| 13 | virsh undefine <hostname> | remove the virtual host definition from system |
=== Annotations to some commands ===
== commands 7.) und 8.) virsh suspend/resume ==
When using these commands the clock of the virtual host is updated after execution of ''virsh resume''.
== commands 9.) und 10.) virsh save/restore ==
When using these commands the clock of the virtual host is not updated after execution of ''virsh restore''.
The clock of the vhost has to be updated by one of the following methods:
  * ntpdate:		sudden time change – can lead to problems with applications
  * ntp service: 	slow time change - can take a rather long time
The command combination virsh save/restore is best suited in order to stop all vhosts on a KVM host, reboot the KVM host and restart all vhosts again
== command 11.) virsh dumpxml ==
Reconfiguring a running vhost from the command line with ''virsh'' commands only changes the vhost configuration in the memory of the KVM host. After a restart of the vhost the configuration is still valid that was valid before the reconfiguration and that was stored on the hard disk.\\ 
In order to store configuration changes done from the command line persistently, the host definition file has to be updated. The file is stored in the folder '/etc/libvirt/qemu' and normally uses the file name '<vhostname>.xml'. The file update for the vhost 'vhostname' can be done like so:
  root@kvm55:~# cd /etc/libvirt/qemu
  root@kvm55:~# virsh dumpxml vhostname --inactive >vhostname.xml
It is safe to update the file while the vhost is running, because the file is only read at vhost start-up. 
== command 12.) virsh define ==
When in contradiction to command 11.) the xml configuration file of a running vhost in folder '/etc/libvirt/qemu' is changed, the current settings of a running vhost in memory are not changed. When the changes should not only be valid after a shutdown/reboot, the changed vhost definition has to be read into the memory of the KVM host. This is done by the command ''virsh define'': 
  root@kvm55:~# cd /etc/libvirt/qemu
  root@kvm55:~# virsh define vhostname vhostname.xml
It is save to execute the command while the affected vhost is running. Some configuration changes are not possible while the vhost is running and therefore are not carried out. These changes become only valid after a shutdown/reboot. Changes of a xml file with the following execution of ''virsh define'' behave identical here with respect to vhost configuration changes by the VMM GUI.\\ 
\\ 
[[public:kvm:access|previous chapter]] | [[public:kvm:access|contents]] | [[public:kvm:access:local_vhost|next chapter]]