Re: Some confusion with flock.

[Jeffrey Walton <noloader@gmail.com>]

On Thu, Oct 23, 2025 at 3:29 PM Tim Woodall <debianuser@woodall.me.uk> wrote:
>
> On Thu, 23 Oct 2025, Tim Woodall wrote:
>
> >    exec {FDLOCK}>&-
>
> vs flock -u ${FDLOCK}
>
> I actually managed to get chatGPT to explain this (eventually).
>
> The former closes the file, but doesn't release the lock, the lock is
> released only when the process exits and the OS determines that it's
> safe to release the lock.
>
> flock -u unconditionally releases the lock.
>
>
> Turns out that closing the FD was the old BSD way of doing it and it's
> still habit in a lot of code where it doesn't matter. It's only cases
> like mine where the os cleanup gets delayed that the explicit flock -u
> is now needed.
>
> (Also from chatGPT, so may not be correct!)

You might try using Shellcheck.  It may flag the use case.

Jeff