[Info-vax] Orphaned processes on OpenVMS

[Johnny Billquist]

On 2011-05-25 19.01, Wendell wrote:
> On May 23, 6:08 am, koeh... at eisner.nospam.encompasserve.org (Bob
> Koehler) wrote:
>> In article<ir740v$3l... at Iltempo.Update.UU.SE>, Johnny Billquist<b... at softjar.se>  writes:
>>
>>     The only thing I've heard substantially influenced by UNIX, and also
>>     attempted various ways in earlier DEC operating systems, was the
>>     now ubiquitous nesting of directories inside directories in a file
>>     hierarchy.  Even then, there were influences that lead VMS to a
>>     per-disk hierarchy, rather than UNIX style mount points.
>
> What were the perceived advantages of the per-disk hierarchy? The Unix
> way seems obviously cleaner to me, but it seems that Darwin/OS X has
> gone over to something more like VMS.

Well, you do get into the obvious problems of interdependency when you 
have mount points inside the file system. You cannot unmount disk a, 
because you have disk b mounted on disk a.

Also, in VMS, mounting is a somewhat different process and concept than 
in Unix. You mount a device in order to do any I/O to it. It also means 
that just because one user have a disk mounted, that don't mean that 
another user can do I/O on it. It can be private to only you.
Which brings up another important point, where Unix perhaps isn't that 
good. Bringing your own disk to a machine and mounting it. Under VMS, 
any user can do this. There are no security issues or other problems 
with that. Mounting is not a privileged operation.
In Unix, this is a big no-no.

And, of course, also tapes can be mounted under VMS. Not so, under Unix, 
where mounting is totally tied into the disk file system area.

And mounting needs to be done under VMS, even if there is no file system 
on the disk. Mounting is basically just the process of allowing I/O to a 
device. When it is unmounted, you can remove the device. When it is 
mounted, you can not. To create a file system on a disk, you need to 
mount the disk first (but telling VMS that there is no file system to 
try to understand).

So I'd say there are several advantages.

But YMMV. It's closely related to the question of whether devices should 
exist in the file system or not as well.

	Johnny