[Info-vax] Request description of UFS for VMS person

[Michael Moroney]

AEF <spamsink2001 at yahoo.com> writes:

>Then there's the mysterious VMS deletion process which I'd love to
>learn. I only know about it from the strange ANAL/DISK errors about
>file headers being busy, deleted, quasi-deleted, or whatever. I'd love
>to learn about that too. [Fuzzy-memory-of-a-long-ago-event alert!] I
>once learned a little about it and kept a sample lying around, but
>it's been so long I can't recall just what that was! Wait, I think it
>was a file header without a filename being entered in any directory.
>If I have time I'll try to resurrect this. [Another fuzzy-memory-of-a-
>long-ago-event alert!] I think I even asked this question (re the file-
>deletion process) here once many years ago and if I did I never got a
>good answer.

Yes, on VMS a file can exist without being in any directory.  By speaking
the right magic to RMS a program can create a file not in any directory.
It can be pre-deleted as well, see below.  The file exists because a
header in INDEXF.SYS says it does.

There is a bit in the file header that says the file has been deleted.
It exists for valid files.  This may seem to be a contradiction, but the
bit really means "delete this file when the last accessor closes this 
file".  This bit being set causes ANALYZE/DISK to complain.

What the familiar $ DELETE command really does is to open the file, set 
the deleted file bit and close it.  99.9% of the time the DELETE command
is the only thing accessing the file, so it is the last (only) accessor
of it when DELETE closes the file.  It is here that the file system does
the real deletion of the file (frees the header, used blocks etc).
If some other program also has the file open, the file is _not_ deleted
when DELETE closes it.  It will be deleted when it (or the last accessor)
closes it.  If the system crashes, the file is never closed and lives on
as a zombie file, not in any directory, supposed to be deleted but still
there, until $ ANALYZE/DISK finds it and /REPAIR does something about it.

RMS can create files not in any directory.  This is normally used for
temporary files.  By setting the deleted file bit these files are 
automatically deleted on a close (including abnormal termination) so this
is useful to keep the file system clean.