The boot loader configuration file boot.cfg specifies the kernel, the kernel options, and the boot modules that the mboot.c32 or mboot.efi boot loader uses in an ESXi installation.

The boot.cfg file is provided in the ESXi installer. You can modify the kernelopt line of the boot.cfg file to specify the location of an installation script or to pass other boot options.

The boot.cfg file has the following syntax: 
# boot.cfg -- mboot configuration file
#
# Any line preceded with '#' is a comment.

title=STRING
prefix=DIRPATH
kernel=FILEPATH
kernelopt=STRING
modules=FILEPATH1 --- FILEPATH2... --- FILEPATHn

# Any other line must remain unchanged.

The commands in boot.cfg configure the boot loader.

Table 1. Commands in boot.cfg.
Command Description
title=STRING Sets the boot loader title to STRING.
prefix=STRING (Optional) AddsDIRPATH/ in front of every FILEPATH in the kernel= and modules= commands that do not already start with / or with http://.
kernel=FILEPATH Sets the kernel path to FILEPATH.
kernelopt=STRING Appends STRING to the kernel boot options.
modules=FILEPATH1 --- FILEPATH2... --- FILEPATHn Lists the modules to be loaded, separated by three hyphens (---).

See Create an Installer ISO Image with a Custom Installation or Upgrade Script and PXE Booting the ESXi Installer.