# Hibernate

* When you hibernate an instance, **EC2 signals the operating system to perform hibernation (suspend-to-disk)**.<br>

* Hibernation **saves the contents from the instance memory (RAM) to your Amazon EBS root volume**.<br>

* **EC2 persists the instance's EBS root volume and any attached EBS data volumes**.<br>

* When you start your instance:

  * The **EBS root volume is restored to its previous state**.
  * The **RAM contents are reloaded**.
  * The **processes that were previously running on the instance are resumed**.
  * **Previously attached data volumes are reattached** and the **instance retains its instance ID**.

* It **can be useful for long-running applications**, which **need to save the RAM state** or **services which take a lot of time to initialise**.

## Limitations

* Supported instance families:
  * C3, C4, C5
  * I3
  * M3, M4, M5, M5a, M5ad
  * R3, R4, R5, R5a, R5ad
  * T2, T3, T3a<br>
* Instance RAM:
  * **RAM size must be less than 150 GB**.<br>
* Instance size:
  * It is **not supported for bare metal instances**.