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This was in a mount namespace, so it was not shared, If it was not shared, then this seems like a bug. Please, say me reproduction steps, I will try to fix the bug. If you don't have reproduction steps, then, at very least, say something like "this happens at line xxx of this big program". Also, note that "unshare(CLONE_NEWNS)" and "unshare --mount" behave differently: if you do "unshare(CLONE_NEWNS)", then all shared mounts continue to be shared. But if you do "unshare --mount", then it internally does "unshare(CLONE_NEWNS)" and then equivalent of "mount --make-rprivate", i. e. makes all mounts inside new namespace private. > it was a new image, so not shared either, and '/' was not involved at When you make a new mount under existing shared mount, it becomes shared, too. (I just checked this.) Also, on systemd, all mounts (not only '/') are shared by default, I just checked this, too. -- Askar Safin