This Summer will mark 30 years since I first laid hands on a unix-like system. I probably was introduced to unix mount points very shortly after starting in the unix world which reminded me a lot of MSDOS except that there aren't nearly as many gotchas and things worked like one would dream they should work so I was probably introduced to the concept of the mount point somewhere in those early days.
I may just be remembering things the wrong way but it seems like that for most of my memory, one could be root and, if you cd'd to a mount point, one could mount /dev/whatever on that mount point and immediately see the top of the new tree you had just mounted. If you cd'd in to that tree and tried to umount, you got the error that the file system was busy which makes sense because you are trying to saw off the limb you are sitting on, so to speak. If you cd'd out of the mount point and nobody else was in it, you could umount and all was well. I accidentally discovered now that I can become the root user, cd to a mount point and mount something with a subsequent ls of my current directory yielding nothing new. One doesn't see the new mount. If you open another session and look at the mount point, the new mount is there. You can even create a file under the new mount which is only visible to you if you didn't cd out of the mount point. Everybody else who looks at that point will see what's mounted there and not the test file slipped in under the mount. Has this always been the normal behavior of mount or has there been a change? I see this behavior as being useful like self-modifying code which is usually a huge thing to avoid but it was kind of interesting to notice. Martin McCormick