Sending a Diagnostic Interrupt

Caution

This feature is for advanced users. Sending a diagnostic interrupt to a live system can cause data corruption or system failure.

You can send a diagnostic interrupt to troubleshoot an unresponsive or unreachable compute virtual machine (VM) instance.

A diagnostic interrupt causes the instance's OS to crash and reboot. Before you send a diagnostic interrupt, you must configure the OS to generate a crash dump (also called a memory dump file) when it crashes. The crash dump captures information about the state of the OS at the time of the crash. After the OS restarts, you can analyze the crash dump to identify and debug the issue.

Required IAM Policy

To use Oracle Cloud Infrastructure, you must be granted security access in a policy by an administrator. This access is required whether you're using the Console or the REST API with an SDK, CLI, or other tool. If you get a message that you don’t have permission or are unauthorized, verify with your administrator what type of access you have and which compartment to work in.

For administrators: The policy in Let users launch compute instances includes the ability to send a diagnostic interrupt to an instance. If the specified group doesn't need to launch instances or attach volumes, you could simplify that policy to include only manage instance-family, and remove the statements involving volume-family and virtual-network-family.

If you're new to policies, see Getting Started with Policies and Common Policies. For reference material about writing policies for instances, cloud networks, or other Core Services API resources, see Details for Core Services.

Before You Begin

The instance's OS must be configured to generate a crash dump file.
The instance must be in the Running state. For more information, see Stopping, Starting, or Restarting an Instance.
There are no in-progress actions affecting the instance, such as block volumes or secondary VNICs in the process of being attached or detached.

Configuring the OS to Generate a Crash Dump

Before you send a diagnostic interrupt to an instance, you must configure the OS to generate a crash dump when it crashes. The diagnostic interrupt is received as a non-maskable interrupt (NMI) on the target instance.

The steps depend on the OS.

Linux

Note

On Oracle Linux platform images, the OS is either fully configured or partially configured to generate a crash dump, depending on the image release date.

Oracle Linux 8

Images released in August 2020 or later: The image is fully configured to generate a crash dump.
Earlier images: The dump-capture kernel is installed and configured, but you must perform the other configuration steps.

Oracle Linux 7

Images released in August 2020 or later: The image is fully configured to generate a crash dump.
Earlier images: The dump-capture kernel is installed and configured, but you must perform the other configuration steps.

Oracle Linux 6

Images released in September 2020 or later: The image is fully configured to generate a crash dump.
Earlier images: The dump-capture kernel is installed and configured, but you must perform the other configuration steps.

Connect to the instance.
Install and configure the dump-capture kernel:
1. Install kdump and kexec by running the following command:
```
sudo yum install kexec-tools
```
2. Reserve memory on the kernel to save the crash dump. Do the following:
  1. Open the etc/default/grub file in a text editor.
  2. In the line that starts with GRUB_CMDLINE_LINUX_DEFAULT, add the parameter crashkernel=<memory-to-reserve>. For example, to reserve 100 MB, add crashkernel=100M.
  3. Save the changes and close the file.
  4. Rebuild the GRUB file by running the following command:
```
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
```
Configure the kernel to crash when it receives a diagnostic interrupt. To do this, open the /etc/sysctl.conf file in a text editor and add the following line:
```
kernel.unknown_nmi_panic=1
```
Apply the change to /etc/sysctl.conf by running the following command:
```
sysctl -p
```

Windows Server - Platform Image

If you use a Windows Server platform image that was released in April 2020 or later, the image is already configured to generate a crash dump.

If you use an image that was released before April 2020, do the following:

Connect to the instance.
Download the Oracle VirtIO Drivers for Microsoft Windows.
Install the drivers and then restart the instance.

Windows Server - Customer-Provided Image

Refer to the third-party documentation for your operating system for more information.