Host fails to mount root file system during boot
search cancel

Host fails to mount root file system during boot


Article ID: 308604


Updated On:


VMware vSphere ESXi


This article provides steps to recover a host that does not boot because it cannot find the root file system.

  • Host does not boot normally.
  • A kernel panic error is generated.
  • You see a message similar to:

    Kernel Panic: VFS: : unable to mount root fs on 00:00"
    Please append a correct "root=" boot option


VMware ESX 4.0.x
VMware ESX Server 3.5.x
VMware ESX 4.1.x
VMware ESX Server 3.0.x


This issue is most commonly caused by a misconfiguration of the boot parameters or a change in drivers that did not get updated correctly.
To ensure that the boot parameters and drivers are correctly updated:
  1. Reboot the host.
  2. At the grub loader prompt select Service Console-troubleshooting mode (ESX 3.x) or Troubleshooting Mode (ESX 4.x). This may allow you to boot and enter the system.

    Note: In cases where the system does not boot in this mode, file a support request with VMware Support and note this Knowledge Base article ID in the problem description. For more information on filing a support request, see How to Submit a Support Request .

  3. Log in to the Service Console as the user root .
  4. Run these commands, according to your respective version of VMware ESX.

    VMware ESX 3.x

    1. Run this command to update the known PCI settings:

      esxcfg-boot -p

    2. Run this command to update the boot settings:

      esxcfg-boot -b

    3. Run this command to reinitialize the boot files:

      esxcfg-boot -r

    VMware ESX 4.x

    Run this command:

    esxcfg-boot -b

    Note: The additional steps under VMware ESX 3.x are no longer required in VMware ESX 4.x.
  5. Run this command to reboot the host:

    shutdown -r now

  6. Select the default boot menu option.

Additional Information

If running the esxcfg-boot -b command fails, run vdf -h on the host to see how much free space is available in /boot. If there is very little space, such as 100 MB or less, check the /tmp and /vmimages folder for any old files or very large ISOs and remove them. Re-run esxcfg-boot -b. If you are able to run this command, reboot the host.
Note: ESX requires at least 24MB to boot properly.
You may also experience this issue after a successful upgrade (such as upgrading from ESX 3.5 to 4.0 and then performing an upgrade from 4.0 to 4.1). To resolve this issue, go to the troubleshooting mode and then run this command to clean the old ESX 3.5.x files:
cleanup-esx3 –f
However, after using this command, you cannot revert to ESX 3.5.x.
Note: VMware High Availability agents may not correctly configure after the failure to boot and in the Summary tab, you can see that the HA configuration failed. In this case, in vCenter Server, right-click the host and click Reconfigure HA.

ESX fails to boot with the error: Error 15: Could not find file
Troubleshooting an ESX host that does not boot