Before you begin

• If you want to log serial port output in Cloud Logging, familiarize yourself withCloud Logging.
• If you haven't already, set upauthentication. Authentication verifies your identity for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

  Select the tab for how you plan to use the samples on this page:

  Console

  When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.

  gcloud

  1. Install the Google Cloud CLI. After installation,initialize the Google Cloud CLI by running the following command:

     gcloudinit

     If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity.

     Note: If you installed the gcloud CLI previously, make sure you have the latest version by runninggcloud components update.
  2. Set a default region and zone.

  REST

  To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

  Install the Google Cloud CLI. After installation,initialize the Google Cloud CLI by running the following command:

  gcloudinit

  If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity.

  Note: If you installed the gcloud CLI previously, make sure you have the latest version by runninggcloud components update.

  For more information, seeAuthenticate for using REST in the Google Cloud authentication documentation.

Kernel panic

A kernel panic can happen when the kernel is unable to load properlyinitramfsmodules, which are required for the guest OS to boot.

Another form of kernel panic can occur in a situation where the kernel doesn'tknow how to handle a certain request and protects itself by stopping.Kernel panic can happen on a Compute Engine VM running RedHat, SUSE, CentOS,or Ubuntu.

Common error messages

Below are some of the most common kernel panic events for reference:

Kernel panic - not syncing: hung_task: blocked tasks

Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Kernel panic - not syncing: NMI: Not continuing

Kernel panic - not syncing: out of memory. panic_on_oom is selected

Kernel panic - not syncing: Fatal Machine check

Common causes

The kernel panic error can occur due to multiple reasons. Some of thecommon reasons are:

• The entry related to theinitramfs file that corresponds to the kerneldoesn't exist in thegrub.cfg file.
• Theinitramfs file doesn't get generated in the/boot directory duringkernel installation.
• Theinitramfs file gets only partially generated or is corrupted.

Symptoms

When you experience kernel panic on a VM instance, a common symptom is that thekernel does not allow you to connect to the VM, even when using the serialconsole.

You should check the serial console logs to identify the kernel that was loadedby the guest OS, for example:

[    0.000000] Initializing cgroup subsys cpu[    0.000000] Initializing cgroup subsys cpuacct[    0.000000] Linux version 3.10.0-1160.95.1.el7.x86_64 (mockbuild@x86-vm-42.build.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-44) (GCC) ) #1 SMP Thu Aug 10 10:46:21 EDT 2023

The following example shows a kernel panic event due toinitramfs issues:

[    1.520840] No filesystem could mount root, tried:[    1.520840][    1.521964] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)[    1.523495] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 3.10.0-1160.95.1.el7.x86_64 #1[    1.524932] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022[    1.526901] Call Trace:[    1.527421]  dump_stack+0x41/0x60[    1.527978]  panic+0xe7/0x2ac[    1.528578]  mount_block_root+0x2be/0x2e6[    1.529693]  ? do_early_param+0x95/0x95[    1.530441]  prepare_namespace+0x135/0x16b[    1.531237]  kernel_init_freeable+0x203/0x22d[    1.532081]  ? rest_init+0xaa/0xaa[    1.532808]  kernel_init+0xa/0x103[    1.533395]  ret_from_fork+0x35/0x40[    1.535229] Kernel Offset: 0x23a00000 from 0xffffffff81000000

Resolve the kernel panic error

To resolve the kernel panic error, perform the following steps:

1. Connect to theserial consoleand log in to the VM from the Google Cloud console.

2. ClickReset for VM in the Google Cloud console.

3. After the GRUB splash screen appears, select the previously workingkernel or rescue kernel, and then boot the system. This causes the VMto start with the selected kernel.

   

   Note: Booting the VM by selecting the previous kernel from the GRUB splashscreen doesn't make changes to GRUB configuration file, so this is not apersistent change.

4. When the VM is accessible, you can initiate an SSH connection to the VM.

5. Identify the cause of the issue and take further action accordingly.

   For example, if theinitramfs file is missing or corrupted,complete the following steps:

   1. Generate theinitramfs file corresponding to original kernel by usingthedracut command:

      dracut -f /boot/initramfs-KERNEL_VERSION.imgKERNEL_VERSION

      ReplaceKERNEL_VERSION with the VM's currentkernel version. For example,3.10.0-1160.95.1.el7.x86_64.

   2. Update thegrub2.cfg file using thegrub2-mkconfig command, forexample:

      grub2-mkconfig -o /boot/grub2/grub.cfg

   3. After theinitramfs file is generated, you can restart the VM withoutany errors.