I have been using containers from nvcr.io (like nvidia/cuda:11.0.3-base-ubuntu20.04) and docker hub (like deepops/nccl-tests-tf20.06-ubuntu18.04) and run them with docker or enroot (via slurm). I find that there are some binaries from the host system mounted in these containers like this
/dev/mapper/ubuntu–vg-ubuntu–lv on /usr/bin/nvidia-smi type ext4 (ro,nosuid,nodev,relatime)
When I run these containers with singularity (via slurm) these mounts are missing. Mostly for educational purposes I want to know how these mounts are done and why singularity behaves differently from docker/enroot.