Software can't write to share after update to 25.10

TrueNAS General
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Hi there,

we do encounter a somewhat strange issue with some of our TrueNAS systems in combination with Avid Media Composer.

When trying to create a new project on a network share (which essentially creates a bunch of folders and files) it will fail creating those files on one system (the only one without a connected ad for authentication) even foldes won’t work. Creating files and folders manually from the explorer works.

Also upon investigation we found out, that files and folders created by media composer do not get the correct permissions (only “everyone”) even though they should inherit permissions (and manually created files do as expected).

We now have one box with 25.04 where we are still able to create projects, one box where it was possible until the upgrade to 25.10 and one box we started with 25.10 with where it never worked.

So my hypothesis is that something changed (possibly with the changes in SMB from .04 to .10) that now does not tolerate media composers permission behaviour anymore. Did someone else also encounter this or knows what to do about it? All of our settings between the the boxes seem to be the same regarding ACLs and dataset setup.

Thanks in advance for your help!

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SMB clients can modify permissions set server-side during or after file creation. It might be worth getting a pcap of behavior and see what’s failing there.

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I captured it with wireshark but I honestly have no idea what I am looking for.

As far as I understand it, permissions are indeed altered/set and when compared to creating a folder in windows explorer, the access mask is different.

But what I still don’t understand: this has been the way that software behaved for a long time. What has changed now?

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Major samba version change perhaps. If you want to you can PM me wireshark output (assuming it’s reasonably small) and I can take a brief glance at it. There’s some potential it’s relying on some surprising workflow to create secure temporary files or something. E.g. Hyrum’s law:

With a sufficient number of users of an API, it does not matter what you promise in the contract: all observable behaviors of your system will be depended on by somebody.

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