rdinit=/bin/sh and manually booted the system (in chroot) from command line, complete with mounted filesystems, network services and X desktop. The init is still busybox's /bin/sh.
The problem is that I see many uncollected "zombie" processes.
How to start proper init, but not all boot scripts again? I feel that if I "exec chroot /mnt /sbin/init" then it either starts extra things or exit with some error and "kernel panic".
(Don't advice just to reboot)
Update: Just executed into system bash (instead of busybox's one)
exec chroot /mnt /bin/bash and now zombies gone.