Looks like you're right. I think cherry-picking that sort of change to debootstrap several years into a stable release is rather too risky, but I'm testing (in xenial this time!) a change to fix up /dev/ptmx in livecd-rootfs.
Looks like you're right. I think cherry-picking that sort of change to debootstrap several years into a stable release is rather too risky, but I'm testing (in xenial this time!) a change to fix up /dev/ptmx in livecd-rootfs.