umount /chrootedpath /dev/pts after several chroot(s): target is busy

I've been doing several chrooted environments in parallel, each in separate folder (when the script with chroot exited I sometimes run another in same folder), and for a while it seemed fine. But now I have almost empty /dev of "main" system (cannot start apps/open new windows, etc.). I've been mounting like this: sudo mount -t proc proc $work_path/fin_sq/proc sudo mount -t sysfs sys $work_path/fin_sq/sys sudo mount -t devtmpfs devtmpfs $work_path/fin_sq/dev sudo mount -t devpts devpts $work_path/fin_sq/dev/pts and unmounting after exiting chroot: umount "${work_path}"/fin_sq/dev/pts umount "${work_path}"/fin_sq/dev umount "${work_path}"/fin_sq/proc umount "${work_path}"/fin_sq/sys Occasionally I've interrupted script running in chrooted environment via ctrl-c. For cases when the script run in a folder where there were remnants of previous run, the script is coded to umount and delete previous work. Today I saw target is busy at least in one terminal window where I run script with chroot. After umount failed the script deleted all folders of chrooted system. For the future, I think I better cancel further unmounts/deletions if one of umounts fails. However, what do you think might cause such result? How to investigate? How to get system to working condition? I'm not rebooting the system for a while hoping to learn Linux deeper. TIA P.S. full script(s) for those interested: script running other script via chroot , searching for /dev/pts finds two lines (mount/umount) in the code. "Naturally" lsof shows empty output and adding --force seems to make no difference. Trying mount -t devpts devpts /dev resulted in "devtmpfs already mounted on one_of_chrooted_paths/dev". I've read https://unix.stackexchange.com/questions/464585/umount-target-is-busy , but the question is for -o rbind, I mount w/out it. Again, it was working with two chrooted, I increased to 3-4 and something broke...