unshare -m -u -i -n -p -f /bin/execlineb -c 'fdmove -c 3 0 pipeline -d { /root/ns_execline /mnt/data/fsb2/work/05acf558e384806c252300f522788bd9f0055b5774266efabf965915d22be30b.alpine-base -u :1000:100 /bin/sh -i } execlineb /dev/stdin'

This currently needs statically linked (preferrably not against glibc) execline, busybox *and* runit. It should make use of sigrelay1 instead whenever that will be ready.