ubuntu-22.04: works on laptop.

decrypt-root-with-usb/ubuntu-20.04/usr/share/initramfs-tools/scripts/local-top/cryptroot

 #!/bin/sh
 
+# Search for cryptkey.txt
+
 PREREQ="cryptroot-prepare"
 
 #
@@ -171,9 +173,11 @@ setup_mapping() {
 		echo -n "Searching for cryptkey.txt on available disks... "
 		local partition
 		for partition in `cat /proc/partitions |awk '{print $4}'|tail -n +3`; do
-		    if mount /dev/$partition /mnt 2>/dev/null; then
+		    echo -n " $partition"
+		    if mount -oro /dev/"$partition" /mnt 2>/dev/null; then
+			echo -n "(mounted)"
 			cat /mnt/cryptkey.txt >> /tmp/cryptkeys.txt 2>/dev/null
-			umount /dev/$partition
+			umount /dev/"$partition"
 		    fi
 		done
 		echo "done."

decrypt-root-with-usb/ubuntu-22.04/usr/share/initramfs-tools/scripts/local-top/cryptroot

+#!/bin/sh
+
+# Search for cryptkey.txt
+
+PREREQ="cryptroot-prepare"
+
+#
+# Standard initramfs preamble
+#
+prereqs()
+{
+	# Make sure that cryptroot is run last in local-top
+	local req
+	for req in "${0%/*}"/*; do
+		script="${req##*/}"
+		if [ "$script" != "${0##*/}" ]; then
+			printf '%s\n' "$script"
+		fi
+	done
+}
+
+case $1 in
+prereqs)
+	prereqs
+	exit 0
+	;;
+esac
+
+. /scripts/functions
+
+[ -f /lib/cryptsetup/functions ] || return 0
+. /lib/cryptsetup/functions
+
+
+# wait_for_source()
+#   Wait for encrypted $CRYPTTAB_SOURCE . Set $CRYPTTAB_SOURCE
+#   to its normalized device name when it shows up;
+#   return 1 if timeout.
+wait_for_source() {
+    wait_for_udev 10
+
+    if crypttab_resolve_source; then
+        # the device is here already, no need to loop
+        return 0
+    fi
+
+    # If the source device hasn't shown up yet, give it a little while
+    # to allow for asynchronous device discovery (e.g. USB).
+    #
+    # We also need to take into account RAID or other devices that may
+    # only be available on local-block stage. So, wait 5 seconds upfront,
+    # in local-top; if that fails, end execution relying on local-block
+    # invocations. Allow $ROOTDELAY/4 invocations with 1s sleep times (with
+    # a minimum of 20 invocations), and if after that we still fail, then it's
+    # really time to give-up. Variable $initrd_cnt tracks the re-invocations.
+    #
+    # Part of the lines below has been taken from initramfs-tools
+    # scripts/local's local_device_setup(), as suggested per
+    # https://launchpad.net/bugs/164044 .
+
+    local slumber=5
+    if [ "${CRYPTROOT_STAGE-}" = "local-block" ]; then
+         slumber=1
+    fi
+
+    cryptsetup_message "Waiting for encrypted source device $CRYPTTAB_SOURCE..."
+
+    while [ $slumber -gt 0 ]; do
+        sleep 1
+
+        if [ -x /scripts/local-block/lvm2 ]; then
+            # activate any VG that might hold $CRYPTTAB_SOURCE
+            /scripts/local-block/lvm2 "$CRYPTTAB_SOURCE"
+        fi
+
+        if crypttab_resolve_source; then
+            wait_for_udev 10
+            return 0
+        fi
+
+        slumber=$(( $slumber - 1 ))
+    done
+    return 1
+}
+
+# setup_mapping()
+#   Set up a crypttab(5) mapping defined by $CRYPTTAB_NAME,
+#   $CRYPTTAB_SOURCE, $CRYPTTAB_KEY, $CRYPTTAB_OPTIONS.
+setup_mapping() {
+    local dev initrd_cnt
+
+    # We control here the number of re-invocations of this script from
+    # local-block - the heuristic is $ROOTDELAY/4, with a minimum of 20.
+
+    if [ -f "$CRYPTROOT_COUNT_FILE" ]; then
+        initrd_cnt="$(cat <"$CRYPTROOT_COUNT_FILE")"
+    else
+        initrd_cnt="${ROOTDELAY:-180}"
+        initrd_cnt=$(( initrd_cnt/4 ))
+        if [ $initrd_cnt -lt 20 ]; then
+            initrd_cnt=20
+        fi
+        echo "$initrd_cnt" >"$CRYPTROOT_COUNT_FILE"
+    fi
+
+    # The same target can be specified multiple times
+    # e.g. root and resume lvs-on-lvm-on-crypto
+    if dm_blkdevname "$CRYPTTAB_NAME" >/dev/null; then
+        return 0
+    fi
+
+    crypttab_parse_options --export --missing-path=fail || return 1
+
+    if ! wait_for_source; then
+        if [ $initrd_cnt -eq 0 ]; then
+            # we've given up
+            if [ -n "$panic" ]; then
+                panic "ALERT! encrypted source device $CRYPTTAB_SOURCE does not exist, can't unlock $CRYPTTAB_NAME."
+            else
+                # let the user fix matters if they can
+                echo "	ALERT! encrypted source device $CRYPTTAB_SOURCE does not exist, can't unlock $CRYPTTAB_NAME."
+                echo "	Check cryptopts=source= bootarg: cat /proc/cmdline"
+                echo "	or missing modules, devices: cat /proc/modules; ls /dev"
+                panic "Dropping to a shell."
+            fi
+            return 1 # can't continue because environment is lost
+        else
+            initrd_cnt=$(( initrd_cnt - 1 ))
+            echo "$initrd_cnt" >"$CRYPTROOT_COUNT_FILE"
+            return 0 # allow some attempts on local-block stage
+        fi
+    fi
+
+    # our `cryptroot-unlock` script searches for cryptsetup processes
+    # with a given CRYPTTAB_NAME it their environment
+    export CRYPTTAB_NAME
+
+    if [ -z "${CRYPTTAB_OPTION_keyscript+x}" ]; then
+        # no keyscript: interactive unlocking, or key file
+
+        if [ "${CRYPTTAB_KEY#/FIXME-initramfs-rootmnt/}" != "$CRYPTTAB_KEY" ]; then
+            # skip the mapping for now if the root FS is not mounted yet
+            sed -rn 's/^\s*[^#[:blank:]]\S*\s+(\S+)\s.*/\1/p' /proc/mounts | grep -Fxq -- "$rootmnt" || return 1
+            # substitute the "/FIXME-initramfs-rootmnt/" prefix by the real root FS mountpoint otherwise
+            CRYPTTAB_KEY="$rootmnt/${CRYPTTAB_KEY#/FIXME-initramfs-rootmnt/}"
+        fi
+
+        if [ "$CRYPTTAB_KEY" != "none" ]; then
+            if [ ! -e "$CRYPTTAB_KEY" ]; then
+                cryptsetup_message "ERROR: Skipping target $CRYPTTAB_NAME: non-existing key file $CRYPTTAB_KEY"
+                return 1
+            fi
+            # try only once if we have a key file
+            CRYPTTAB_OPTION_tries=1
+        fi
+    fi
+
+    local count=0 maxtries="${CRYPTTAB_OPTION_tries:-3}" fstype vg rv
+    while [ $maxtries -le 0 ] || [ $count -lt $maxtries ]; do
+        if [ -z "${CRYPTTAB_OPTION_keyscript+x}" ] && [ "$CRYPTTAB_KEY" != "none" ]; then
+            # unlock via keyfile
+            unlock_mapping "$CRYPTTAB_KEY"
+        else
+	    if [ -z "${CRYPTTAB_OPTION_keyscript+x}" ]; then
+		# Wait for USB to settle
+		/bin/sleep 3
+
+		# Test all devices
+		mkdir /mnt
+		echo -n "Searching for cryptkey.txt on available disks... "
+		local partition
+		for partition in `cat /proc/partitions |awk '{print $4}'|tail -n +3`; do
+		    echo -n " $partition"
+		    if mount -oro /dev/"$partition" /mnt 2>/dev/null; then
+			echo -n "(mounted)"
+			cat /mnt/cryptkey.txt >> /tmp/cryptkeys.txt 2>/dev/null
+			umount /dev/"$partition"
+		    fi
+		done
+		echo "done."
+	    fi
+    
+	    if [ -s /tmp/cryptkeys.txt ]; then
+		local keyfound
+                keyfound=0
+                echo Trying keys from cryptkey.txt
+                for key in `cat /tmp/cryptkeys.txt`; do
+                    if echo -n "$key" | unlock_mapping; then
+                        # Found the key
+                        echo Key found in cryptkey.txt
+                        keyfound=1
+                        key=""
+                    fi
+                done
+                # Remove traces of the key
+                rm /tmp/cryptkeys.txt
+                unset key
+		if [ "$keyfound" = "0" ]; then
+                    # Fall back to manual entry
+		    run_keyscript "$CRYPTTAB_KEY" "$count" | unlock_mapping
+		fi
+	    else
+		# unlock interactively or via keyscript
+		run_keyscript "$CRYPTTAB_KEY" "$count" | unlock_mapping
+	    fi
+        fi
+        rv=$?
+        count=$(( $count + 1 ))
+
+        if [ $rv -ne 0 ]; then
+            cryptsetup_message "ERROR: $CRYPTTAB_NAME: cryptsetup failed, bad password or options?"
+            sleep 1
+            continue
+        elif ! dev="$(dm_blkdevname "$CRYPTTAB_NAME")"; then
+            cryptsetup_message "ERROR: $CRYPTTAB_NAME: unknown error setting up device mapping"
+            return 1
+        fi
+
+        if ! fstype="$(get_fstype "$dev")" || [ "$fstype" = "unknown" ]; then
+            if [ "$CRYPTTAB_TYPE" != "luks" ]; then
+                # bad password for plain dm-crypt device?  or mkfs not run yet?
+                cryptsetup_message "ERROR: $CRYPTTAB_NAME: unknown fstype, bad password or options?"
+                wait_for_udev 10
+                /sbin/cryptsetup remove -- "$CRYPTTAB_NAME"
+                sleep 1
+                continue
+            fi
+        elif [ "$fstype" = lvm2 ]; then
+            if [ ! -x /sbin/lvm ]; then
+                cryptsetup_message "WARNING: $CRYPTTAB_NAME: lvm is not available"
+                return 1
+            elif vg="$(lvm pvs --noheadings -o vg_name --config 'log{prefix=""}' -- "$dev")"; then
+                # activate the VG held by the PV we just unlocked
+                lvm lvchange -a ay --sysinit -- "$vg"
+            fi
+        fi
+
+        cryptsetup_message "$CRYPTTAB_NAME: set up successfully"
+        wait_for_udev 10
+        return 0
+    done
+
+    cryptsetup_message "ERROR: $CRYPTTAB_NAME: maximum number of tries exceeded"
+    exit 1
+}
+
+
+#######################################################################
+# Begin real processing
+
+mkdir -p /cryptroot # might not exist yet if the main system has no crypttab(5)
+
+# Do we have any kernel boot arguments?
+if ! grep -qE '^(.*\s)?cryptopts=' /proc/cmdline; then
+    # ensure $TABFILE exists and has a mtime greater than the boot time
+    # (existing $TABFILE is preserved)
+    touch -- "$TABFILE"
+else
+    # let the read builtin unescape the '\' as GRUB substitutes '\' by '\\' in the cmdline
+    tr ' ' '\n' </proc/cmdline | sed -n 's/^cryptopts=//p' | while IFS= read cryptopts; do
+        # skip empty values (which can be used to disable the initramfs
+        # scripts for a particular boot, cf. #873840)
+        [ -n "$cryptopts" ] || continue
+        unset -v target source key options
+
+        IFS=","
+        for x in $cryptopts; do
+            case "$x" in
+                target=*) target="${x#target=}";;
+                source=*) source="${x#source=}";;
+                key=*) key="${x#key=}";;
+                *) options="${options+$options,}$x";;
+            esac
+        done
+
+        if [ -z "${source:+x}" ]; then
+            cryptsetup_message "ERROR: Missing source= value in kernel parameter cryptopts=$cryptopts"
+        else
+            # preserve mangling
+            printf '%s %s %s %s\n' "${target:-cryptroot}" "$source" "${key:-none}" "${options-}"
+        fi
+    done >"$TABFILE"
+fi
+
+# Do we have any settings from the $TABFILE?
+if [ -s "$TABFILE" ]; then
+    # Create locking directory before invoking cryptsetup(8) to avoid warnings
+    mkdir -pm0700 /run/cryptsetup
+    modprobe -q dm_crypt
+
+    crypttab_foreach_entry setup_mapping
+fi
+
+exit 0