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 fileTroubleshooting an ESX host that does not boot