Control default new file permissions with custom umask

[jil24]

It would be very useful to be able to set a custom umask. Currently the default umask for the entire system/user is used and can't be controlled from the GUI.

I need to have "Ignore Permissions" on one of my Syncthing shares in order for it to be usable. However, when running Syncthing via the GUI, this results in it creating new files using Mac OS's default umask, which is 022. This results in new file permissions of 644 and directory permissions of 755. I would like to launch the syncthing process with umask 002, resulting in new file permissions of 664 and directory permissions of 775.

I don't think this needs to be GUI exposed. Could be a hidden preference. What I'm currently doing is running the entire Syncthing.app using a shell script that launches it in a subshell with a custom umask, but this is clunky.

[wenghuiming1987]

The key distinction here is that chmod only fixes files after they are created, while umask changes the default mode Syncthing creates them with.

For the examples you gave:

• base file mode is usually 666, so umask 022 gives new files 644
• base directory mode is usually 777, so umask 022 gives new directories 755
• with umask 002, those become 664 and 775

So the clean fix is exactly what you described: launch the Syncthing process with a configurable umask, rather than trying to repair permissions later. A hidden preference or launch wrapper/env setting would avoid changing global macOS defaults.

Disclosure: I maintain WebUtilsLab, and I made a small browser-local umask calculator to verify cases like 022 vs 002: https://webutilslab.com/umask-calculator/?ref=github