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Subject: Re: Cygwin API to atomically create a new file with an ACL?
To: cygwin AT cygwin DOT com
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On Sat, Nov 15, 2025 at 3:43 PM Thomas Wolff via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
>
> Am 15.11.2025 um 13:58 schrieb Aurélien Couderc via Cygwin:
> > Does Cygwin have an API to atomically create a new file with an ACL?
> >
> > Aurélien
> I don't think there's such an API in POSIX. Instead it's the purpose of
> the directory default ACL entries to support this.
> While the manual pages of setfacl/getfacl are lousy, a fairly lucid
> description is in 7.6. POSIX Access Control Lists | Administration Guide
> | Red Hat Gluster Storage | 3 | Red Hat Documentation
> <https://docs.redhat.com/en/documentation/red_hat_gluster_storage/3/html/administration_guide/sect-posix_access_control_lists>.

That does not help. There are valid use cases, where this becomes
security relevant due race conditions between file creation and
setting of the ACLs.

That's why all mainframe operating systems (and Windows WinNT as VMS
descendant) which support ACLs also support file creation with ACLs as
an argument.

Aurélien
-- 
Aurélien Couderc <aurelien DOT couderc2002 AT gmail DOT com>
Big Data/Data mining expert, chess enthusiast

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