In order to use your existing physical nodes, you have to add them to the system as OpenNebula Hosts. To add a host only its hostname and type is needed. Hosts are usually organized in Clusters, you can read more about it in the Managing Clusters guide.


Before adding a Linux host check that you can ssh to it without being prompt for a password.

Create and Delete Hosts

Hosts are the servers managed by OpenNebula responsible for Virtual Machine execution. To use these hosts in OpenNebula you need to register them so they are monitored and made available to the scheduler.

Creating a host:

onehost create host01 --im kvm --vm kvm
ID: 0

The parameters are:

  • --im/-i: Information Manager driver.
  • --vm/-v: Virtual Machine Manager driver.

To remove a host, just like with other OpenNebula commands, you can either specify it by ID or by name. The following commands are equivalent:

onehost delete host01
onehost delete 0

Showing and Listing Hosts

To display information about a single host the show command is used:

ID                    : 0
NAME                  : server
CLUSTER               : server
STATE                 : MONITORED
IM_MAD                : kvm
VM_MAD                : kvm
LAST MONITORING TIME  : 05/28 00:30:51

TOTAL MEM             : 7.3G
USED MEM (REAL)       : 4.4G
TOTAL CPU             : 400
USED CPU (REAL)       : 28
TOTAL VMS           : 1

TOTAL:                : 468.4G
USED:                 : 150.7G
FREE:                 : 314.7G

MODELNAME="Intel(R) Core(TM) i7-4650U CPU @ 1.70GHz"


NAME                                                      IMPORT_ID  CPU     MEMORY


    ID USER     GROUP    NAME            STAT UCPU    UMEM HOST             TIME
    13 oneadmin oneadmin kvm1-13         runn  0.0   1024M server       8d 06h14

The information of a host contains:

  • General information of the hosts including its name and the drivers used to interact with it.
  • Capacity information (Host Shares) for CPU and memory.
  • Local datastore information (Local System Datastore) if the Host is configured to use a local datastore (e.g. Filesystem in ssh transfer mode).
  • Monitoring Information, including PCI devices
  • Virtual Machines actives on the hosts. Wild are virtual machines actives on the host but not started by OpenNebula, they can be imported into OpenNebula.

To see a list of all the hosts:

onehost list
       0 server          server      1    100 / 400 (25%) 1024M / 7.3G (13%) on
       1 kvm1            kvm         0                  -                  - off
       2 kvm2            kvm         0                  -                  - off

The above information can be also displayed in XML format using -x.

Host Life-cycle: Enable, Disable, Offline and Flush

In order to manage the life cycle of a host it can be set to different operation modes: enabled (on), disabled (dsbl) and offline (off). The different operation status for each mode is described by the following table:

ENABLED (on) Yes Yes Yes The host is fully operational
UPDATE (update) Yes Yes Yes The host is being monitored
DISABLED (dsbl) Yes Yes No Disabled, e.g. to perform maintenance operations
OFFLINE (off) No No No Host is totally offline
ERROR (err) Yes Yes No Error while monitoring the host, use onehost show for the error description.
RETRY (retry) Yes Yes No Monitoring a host in error state

The onehost tool includes three commands to set the operation mode of a host: disable, offline and enable, for example:

onehost disable 0

To re-enable the host use the enable command:

onehost enable 0

Similarly to put the host offline:

onehost offline 0

The flush command will migrate all the active VMs in the specified host to another server with enough capacity. At the same time, the specified host will be disabled, so no more Virtual Machines are deployed in it. This command is useful to clean a host of active VMs. The migration process can be done by a resched action or by a recover delete-recreate action, it can be configured at the /etc/one/cli/onehost.yaml by setting the field default_actions\flush to delete-recreate or to resched. Here is an example:

  - :flush: delete-recreate

Custom Host Tags & Scheduling Policies

The Host attributes are inserted by the monitoring probes that run from time to time on the nodes to get information. The administrator can add custom attributes either creating a probe in the host, or updating the host information with: onehost update.

For example to label a host as production we can add a custom tag TYPE:

    $ onehost update

This tag can be used at a later time for scheduling purposes by adding the following section in a VM template:


That will restrict the Virtual Machine to be deployed in TYPE=production hosts. The scheduling requirements can be defined using any attribute reported by onehost show, see the Scheduler Guide for more information.

This feature is useful when we want to separate a series of hosts or marking some special features of different hosts. These values can then be used for scheduling the same as the ones added by the monitoring probes, as a placement requirement.

Update Host Drivers

When OpenNebula monitors a host, it copies driver files to /var/tmp/one. When these files are updated, they need to be copied again to the hosts with the sync command. To keep track of the probes version there’s a file in /var/lib/one/remotes/VERSION. By default this holds the OpenNebula version (e.g. ‘5.0.0’). This version can be seen in he hosts with a onehost show <host>:

onehost show 0
ID                    : 0

The command onehost sync only updates the hosts with VERSION lower than the one in the file /var/lib/one/remotes/VERSION. In case you modify the probes this VERSION file should be modified with a greater value, for example

In case you want to force upgrade, that is, no VERSION checking you can do that adding --force option:

onehost sync --force

You can also select which hosts you want to upgrade naming them or selecting a cluster:

onehost sync host01,host02,host03
onehost sync -c myCluster

onehost sync command can alternatively use rsync as the method of upgrade. To do this you need to have installed rsync command in the frontend and the nodes. This method is faster that the standard one and also has the benefit of deleting remote files no longer existing in the frontend. To use it add the parameter --rsync:

onehost sync --rsync

Host Information

Hosts include the following monitoring information. You can use this variables to create custom RANK and REQUIREMENTS expressions for scheduling. Note also that you can manually add any tag and use it also for RANK and REQUIREMENTS

Key Description
HYPERVISOR Name of the hypervisor of the host, useful for selecting the hosts with an specific technology.
ARCH Architecture of the host CPU’s, e.g. x86_64.
MODELNAME Model name of the host CPU, e.g. Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz.
CPUSPEED Speed in MHz of the CPU’s.
HOSTNAME As returned by the hostname command.
VERSION This is the version of the monitoring probes. Used to control local changes and the update process
MAX_CPU Number of CPU’s multiplied by 100. For example, a 16 cores machine will have a value of 1600. The value of RESERVED_CPU will be subtracted from the information reported by the monitoring system. This value is displayed as TOTAL CPU by the onehost show command under HOST SHARE section.
MAX_MEM Maximum memory that could be used for VMs. It is advised to take out the memory used by the hypervisor using RESERVED_MEM. This values is subtracted from the memory amount reported. This value is displayed as TOTAL MEM by the onehost show command under HOST SHARE section.
MAX_DISK Total space in megabytes in the DATASTORE LOCATION.
USED_CPU Percentage of used CPU multiplied by the number of cores. This value is displayed as USED CPU (REAL) by the onehost show command under HOST SHARE section.
USED_MEM Memory used, in kilobytes. This value is displayed as USED MEM (REAL) by the onehost show command under HOST SHARE section.
USED_DISK Used space in megabytes in the DATASTORE LOCATION.
FREE_CPU Percentage of idling CPU multiplied by the number of cores. For example, if 50% of the CPU is idling in a 4 core machine the value will be 200.
FREE_MEM Available memory for VMs at that moment, in kilobytes.
FREE_DISK Free space in megabytes in the DATASTORE LOCATION
CPU_USAGE Total CPU allocated to VMs running on the host as requested in CPU in each VM template. This value is displayed as USED CPU (ALLOCATED) by the onehost show command under HOST SHARE section.
MEM_USAGE Total MEM allocated to VMs running on the host as requested in MEMORY in each VM template. This value is displayed as USED MEM (ALLOCATED) by the onehost show command under HOST SHARE section.
DISK_USAGE Total size allocated to disk images of VMs running on the host computed using the SIZE attribute of each image and considering the datastore characteristics.
NETRX Received bytes from the network
NETTX Transferred bytes to the network
WILD Comma separated list of VMs running in the host that were not launched and are not currently controlled by OpenNebula
ZOMBIES Comma separated list of VMs running in the host that were launched by OpenNebula but are not currently controlled by it.

Importing Wild VMs

The monitoring mechanism in OpenNebula reports all VMs found in a hypervisor, even those not launched through OpenNebula. These VMs are referred to as Wild VMs, and can be imported to be managed through OpenNebula. This includes all supported hypervisors, even the hybrid ones.

The Wild VMs can be spotted through the onehost show command:

onehost show 3
ID                    : 3
NAME                  : MyvCenterHost
CLUSTER               : -
STATE                 : MONITORED
                    NAME                            IMPORT_ID  CPU     MEMORY
           Ubuntu14.04VM 4223f951-243a-b31a-018f-390a02ff5c96    1       2048
                 CentOS7 422375e7-7fc7-4ed1-e0f0-fb778fe6e6e0    1       2048

And imported through the onehost importvm command:

onehost importvm 0 CentOS7
onevm list
ID USER     GROUP    NAME            STAT UCPU    UMEM HOST               TIME
 3 oneadmin oneadmin CentOS7         runn    0    590M MyvCenterHost  0d 01h02

After a Virtual Machine is imported, their life-cycle (including creation of snapshots) can be controlled through OpenNebula. However, some operations cannot be performed on an imported VM, including: poweroff, undeploy, migrate or delete-recreate.

The same import mechanism is available graphically through Sunstone. Running and Powered Off VMs can be imported through the WILDS tab in the Host info tab.


Using Sunstone to Manage Hosts

You can also manage your hosts using Sunstone. Select the Host tab, and there, you will be able to create, enable, disable, delete and see information about your hosts in a user friendly way.