Common Technical Questions

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 The CPU priority is the amount of CPU resource a VS is given (you can think of this as its “share percentage” multiplied by the number of cores allocated to that VS). This is a minimum number – you can burst over it, up to 100% multiplied by the number of cores.

For example, you have a compute resource with 3GHz CPU cores. Then: 

100% x 1 core = 3GHz (burstable to 3GHz)

10% x 2 cores = 600MHZ (burstable to 6GHz)

5 % x 4 cores = 600MHz (burstable to 12GHz)

So you can either create one VS with 100% CPU priority on that compute resource, or 5 VSs with 20% CPU priority (or any other combinations with the total of 100%).

 Imagine a compute resource like a grocery store with only two checkouts ( CPU cores). In the afternoon, there are not so many customers (virtual servers) so when someone needs to go to checkout, there is always one available. Later in the night, a queue starts to form and customers have to wait, but some of them push to the front of the queue (100 % priority) whilst all other (1% priority) have to wait patiently for the line ahead to clear. 

Depending on the settings of your cloud, OnApp may allow overselling of cloud resources. For example, OnApp will allow you to create 5 virtual servers with 100% CPU priority/1 CPU core on a compute resource with a 4-core CPU. In this example, OnApp would reduce the guaranteed CPU for each virtual server.

To oversell CPU, make sure that CPU Guarantee is not enabled. To disable this, navigate to Settings > Configuration > Compute Resource Zones > click Edit Zone and uncheck the CPU Guarantee box.

If resource overselling is disabled for your cloud, OnApp will not create virtual servers requiring more CPU resource than is available on the compute resource.

 The CPU Guarantee option in OnApp's Settings > Configuration menu enables or disables CPU overselling. With the CPU Guarantee option enabled, OnApp will not create virtual servers requiring more CPU resource than is available on their compute resource.

 Yes, the CPU priority you can set to virtual server depends on the virtualization type of the compute resource the server is located on:

  • On Xen compute resources, you can set the 1-100 CPU priority value.

  • On KVM compute resources under CentOS 6, you can set the 1-100 CPU priority value.

  • On KVM compute resources under CentOS 5, the CPU priority is 100 by default.

 The virtual server CPU utilization is calculated in the following way:

The chart show the total CPU usage for all the cores of this particular VS for a specified time period.The vertical axis shows the CPU usage percentage (CPU percentage is the core-independent quantity). The horizontal axis defines a time period.

 The CPU unit is an abstract figure that replaces CPU priority.  It is an arbitrary relative value that the host can enter to mark the capacity of the compute resources in a zone. It is the host's responsibility to enter the values per compute resources correctly and logically. You can set the amount of units per compute zone and per each particular compute resource in a zone. If you set the CPU Units per compute zone, then each compute resource in this zone will be assigned the number of units set.  To set different capacity to a particular compute resource, specify the CPU units amount to a required compute resource not a zone. To bill for CPU Units, enable CPU units for a billing plan and set the price per unit.

Each compute resource core within a zone is given a 1000 CPU Units default value when CPU units are enabled per zone.

You cannot use CPU Units for KVM5 compute resources, Baremetal, VMware servers, and load balancers.

 You can change the password on the user profile page. You can access it in two ways:

  • Click your account name at the top of the Control Panel screen.
  • In the Control Panel Users and Groups menu, click the full name of the required user.

On the following page, perform these steps:

  1. Click the Edit button in the upper right corner.
  2. On the page that appears, type the new password in the Login Password fields.
  3. Click Save for the changes to take effect.

 There are two parameters showing the free memory for compute resources. Depending on the compute resource type and the Release resource type parameter, the values calculation will differ. The following table illustrates the calculation.

Release Resource TypeKVMXEN

Memory Guarantee

(the actual free Compute resource memory is calculated. All virtual servers residing on the Compute resource will be able to start.) 

total memory - memory overhead* - zombie VSs - sum of all VSs current memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)free_memory (taken from compute resources table) - sum (memory of stopped VSs on this compute resource)current memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)


(free Compute resource memory is calculated with the ability to use memory over-committing)

current memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)

current memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)N/Acurrent memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)

Only Started VSs

(only the memory of running virtual servers is calculated)

clean_memory - memory_allocated_by_running_vms - memory_allocated_by_building_vms

current memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)clean_memory - memory_allocated_by_running_vms - memory_allocated_by_building_vmscurrent memory statistics on this compute resource (cat /proc/meminfo |grep MemFree)

*Memory Overhead for Compute Resources

Each compute resource has a reserved memory overhead value. This value is pre-configured by default in info_hub.yml.

For KVM compute resource:
default_memory_overhead = 1536

For XEN compute resource:

default_memory_overhead = 400 + 0,024 * total_memory

Once the account is paid, it should be unsuspended immediately. It may take up to 15 minutes before you can access the CP again.
Please note that this happens after setting up a payment with the Finance team, and therefore, the Support team will not be able to help you if it is out of office hours for the Finance team.

No, if you require additional usage of the software, you should purchase the required license directly from

We don't support Citrix XenServer compute resources. However, you can manually import existing XenServer virtual servers to the OnApp cloud

Email our Cloud Architecture Specialists at and they will help you make the right decision.

No, it is not possible to change the resolution.

As a workaround, use the zoom in and zoom out features. Press the following key combinations when accessing the console through the browser:

  • Windows: CTRL+Plus Sign or CTRL+Minus Sign
  • Mac: COMMAND+Plus Sign or COMMAND+Minus Sign