This file is indexed.

/etc/grub.d/20_ipxe is in grub-ipxe 1.0.0+git-20180124.fbe8c52d-0ubuntu2.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

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#! /bin/sh
set -e

. /usr/lib/grub/grub-mkconfig_lib

# iPXE is only supported on x86
case $(dpkg --print-architecture) in
	*i386|*amd64) ;;
	*) exit 0 ;;
esac

prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"

IPXE=/boot/ipxe.lkrn

if test -e "$IPXE" ; then
  IPXEPATH=$( make_system_path_relative_to_its_root "$IPXE" )
  echo "Found iPXE image: $IPXE" >&2
  cat << EOF
menuentry "Network boot (iPXE)" --users "" --class network {
${prepare_boot_cache}
	linux16 $IPXEPATH
}
EOF
fi