try

Dockerfile

@@ -32,6 +32,7 @@ RUN (zcat /usr/src/unionfs-2.2.3_for_2.6.24.diff.gz | patch -p1) && \
 FROM lpenz/debian-lenny-i386-minbase
 WORKDIR /root
 COPY --from=kernel-builder /usr/src/*.deb .
+COPY update-initramfs.sh .
 RUN apt-get update && \
     apt-get -y --force-yes install live-helper genisoimage syslinux squashfs-tools aptitude && \
     apt-get clean

Jenkinsfile

@@ -40,8 +40,12 @@ pipeline {
                         --union-filesystem unionfs \
                         --linux-packages "squashfs-modules-2.6.24 linux-image-2.6.24" \
                         -k retrodebian1
-                    cp /usr/share/live-helper/examples/hooks/update-initramfs.sh config/chroot_local-hooks
-                    cp /root/*.deb config/chroot_local-packages/
+                    
+                    chmod +x /root/update-initramfs.sh
+                    cp /root/update-initramfs.sh config/chroot_local-hooks
+
+                    cp /root/linux-image-*.deb config/chroot_local-packages/
+                    cp /root/squashfs-modules-*.deb config/chroot_local-packages/
 
                     lh_build
 

update-initramfs.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+# This is a hook for live-helper(7) to rebuild the initramfs image.
+# To enable it, copy or symlink this hook into your config/chroot_local-hooks
+# directory.
+#
+# Note: You only want to use this hook if you have modified any initramfs-script
+# during the build and need to refresh the initrd.img for that purpose.
+
+grep -q '^squashfs$' /etc/initramfs-tools/modules 2>/dev/null || \
+        echo squashfs >> /etc/initramfs-tools/modules
+
+for KERNEL in /boot/vmlinuz-*
+do
+        VERSION="$(basename ${KERNEL} | sed -e 's|vmlinuz-||')"
+
+        update-initramfs -k ${VERSION} -t -u
+done