I had my test parameters wrong; '-s' tests for size > 0, '-S' tests for socket, '-L' tests for sym-link. I think the intended test is '-e', file exists; and so the required patch is
tjcw@debian:/usr/lib/live/build$ git diff binary_rootfs.0 binary_rootfs diff --git a/binary_rootfs.0 b/binary_rootfs index af8448d..080ee15 100755 --- a/binary_rootfs.0 +++ b/binary_rootfs @@ -106,7 +106,7 @@ case "${LB_CHROOT_FILESYSTEM}" in dd if=/dev/zero of=chroot/filesystem.${LB_CHROOT_FILESYSTEM} bs=1024k count=0 seek=${REAL_DIM} FAKE_MTAB=false - if ! Chroot chroot "test -s /etc/mtab" + if ! Chroot chroot "test -e /etc/mtab" then Chroot chroot "ln -s /proc/mounts/mtab /etc/mtab" FAKE_MTAB=true tjcw@debian:/usr/lib/live/build$