/lib/live/boot/0030-verify-checksums is in open-infrastructure-system-boot 20161101-lts2-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 | #!/bin/sh
#set -e
Verify_checksums ()
{
	for _PARAMETER in ${LIVE_BOOT_CMDLINE}
	do
		case "${_PARAMETER}" in
			live-boot.verify-checksums=*|verify-checksums=*)
				LIVE_VERIFY_CHECKSUMS="true"
				LIVE_VERIFY_CHECKSUMS_DIGESTS="${_PARAMETER#*verify-checksums=}"
				;;
			live-boot.verify-checksums|verify-checksums)
				LIVE_VERIFY_CHECKSUMS="true"
				;;
		esac
	done
	case "${LIVE_VERIFY_CHECKSUMS}" in
		true)
			;;
		*)
			return 0
			;;
	esac
	_MOUNTPOINT="${1}"
	LIVE_VERIFY_CHECKSUMS_DIGESTS="${LIVE_VERIFY_CHECKSUMS_DIGESTS:-sha512 sha384 sha256 sha224 sha1 md5}"
	_TTY="/dev/tty8"
	log_begin_msg "Verifying checksums"
	cd "${_MOUNTPOINT}"
	for _DIGEST in $(echo ${LIVE_VERIFY_CHECKSUMS_DIGESTS} | sed -e 's|,| |g')
	do
		_CHECKSUMS="$(echo ${_DIGEST} | tr [a-z] [A-Z])SUMS ${_DIGEST}sum.txt"
		for _CHECKSUM in ${_CHECKSUMS}
		do
			if [ -e "${_CHECKSUM}" ]
			then
				echo "Found ${_CHECKSUM}..." > "${_TTY}"
				if [ -e "/bin/${_DIGEST}sum" ]
				then
					echo "Checking ${_CHECKSUM}..." > "${_TTY}"
					# Verify checksums
					/bin/${_DIGEST}sum -c "${_CHECKSUM}" < "${_TTY}" > "${_TTY}"
					_RETURN="${?}"
					# Stop after first verification
					break
				else
					echo "Not found /bin/${_DIGEST}sum..." > "${_TTY}"
				fi
			fi
		done
	done
	log_end_msg
	case "${_RETURN}" in
		0)
			log_success_msg "Verification successfull, rebooting in 10 seconds."
			sleep 10
			# Unmount live-media
			cd /
			umount -f "${_MOUNTPOINT}" > /dev/null 2>&1
			sync
			# Attempt to remount all mounted filesystems read-only
			echo u > /proc/sysrq-trigger
			# Immediately reboot the system without syncing or unmounting filesystems
			echo b > /proc/sysrq-trigger
			;;
		*)
			panic "Verification failed, $(basename ${_TTY}) for more information."
			;;
	esac
}
 |