I'm trying to figure out where the default mount options are set for user-mounted filesystems (e.g., disk images, USB thumbdrives, etc.). I'm working with OS X 10.11 ("El Capitan").

The options I specify for known disk partitions in /etc/fstab are respected when they're mounted automatically at boot time — or even manually via Disk Utility — but I can't seem to set the default mount options for any "unknown" filesystem that gets automounted in /Volumes.

I've tried changing AUTOMOUNTD_MNTOPTS in /etc/autofs.conf and adding options with -o to the ProgramArguments array of /System/Library/LaunchDaemons/com.apple.automountd.plist (which required disabling SIP), but neither change seems to have any effect.

It would seem that some other set of defaults is being used... but where are those defaults defined?

1 Answer 1


If I understand your question, you should have a look into /etc/auto_master

This article explains very well how auto-mount works https://useyourloaf.com/blog/using-the-mac-os-x-automounter/

  • The article in the link was updated in 2020, but I'm convinced that it remains out-of-step with how cifs/smb works today (ver 3+ of the protocol). Why do I say this? The permissions I see on my macOS CLI (ls -l) for my Synology mount are not what I should see. As is typical, Apple's manuals are horribly out of date & the documentation is incomplete. I've recently resolved similar issues on a Linux system w/ the uid= & gid= options. Truly frustrating that Apple commands high prices for their systems, but provide inadequate documentation.
    – Seamus
    Jun 29 at 16:28

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