NFS File Locking

[Rick Stevens]

On Wed, 2007-11-28 at 18:19 -0700, Karl Pearson wrote:
> On Wed, November 28, 2007 12:08 pm, Rick Stevens wrote:
> > On Wed, 2007-11-28 at 09:27 -0800, Waldher, Travis R wrote:
> >> Is there a command I can use to manually lock a file?
> >>
> >>
> >>
> >> My goal is to test NFS file locking with groups greater than 16.
> >
> > I don't know of one, but it wouldn't be hard to write.  You'd need to
> > open the file, lock it via fcntl() (flock() does not work over NFS) and
> > hold the lock until not needed.
> >
> > Remember that if the program exits, the lock would be released.
> 
> Can't you just emacs or vi the file and accomplish the same thing? Just a
> thought to save something or other.

I'm not 100% sure of that.  Typically an editor doesn't take a write
lock on a file.  Rather, the editor makes a work copy of the file which
you edit (which is why editing a large file in vi takes so long to
start...it's making a copy of the file).  Some editors actually just
keep a record of what you did.  If you "quit and discard changes", the
work file or the log of what you did are simply discarded and the
original file is left alone.

When you "exit and save", the old file gets overwritten by the work file
or the edits get played back to modify the file.  So, the only time a
write lock is made on the file is when you commit the edits.

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- Rick Stevens, Principal Engineer             rstevens at internap.com -
- CDN Systems, Internap, Inc.                http://www.internap.com -
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-     Have you noticed that "human readable" configuration file      -
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