Error: Failed to update bootloader: failed to execute mtools command: Disk full during ESXi patching

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• ESXi patching or remediation fails during the bootloader update phase.
• The esxupdate.log contains the following error: esximage.Errors.InstallationError: Failed to update bootloader: failed to execute mtools command: COMMAND: export MTOOLS_SKIP_CHECK=1 && mcopy ... STDERR: Disk full
• Host may boot into "VMware Hypervisor Recovery" mode after a failed update.

Environment

• VMware ESXi 8.0.x
• VMware ESXi 7.0.x

Cause

Insufficient space in the ESXi system storage (locker partition) or temporary ramdisk prevents the mtools utility from writing updated bootloader files to the EFI partition.

Resolution

1. Clear the locker partition packages: rm -rf /locker/packages/*
2. Clear temporary files from the ramdisk: rm -rf /tmp/* rm -rf /var/tmp/*
3. For hosts stuck in recovery mode, perform a manual hard reboot to attempt to load the staged image.
4. Verify available space using df -h.

Additional Information

If the EFI boot partition is structurally corrupted, standard recovery keystrokes will not work. We must safely rewrite the boot partition using the ESXi installation media.

1. Mount the ESXi 8.0.3 Installation Media (ISO) to the server via your out-of-band management console (iLO, iDRAC, etc.).

2. Boot the server from the ISO.

3. Follow the prompts to install/upgrade ESXi.

4. Select your standard boot LUN/disk.

5. CRITICAL: Select the option to Install ESXi, preserve VMFS datastore.

6. Complete the installation and reboot.

This method completely wipes and rebuilds the bootbanks and the EFI partition with fresh 8.0.3 files. It will not touch your VMFS datastores or virtual machine data. You will need to re-add the host to vCenter and reapply its network configurations or Host Profile.