Contains binary data on the last integrity check made using fsck on a disk image. Can be deleted to enable some images to be mounted.
disk image
Contains details of the last checksum of a disk image, performed using hdiutil verify, which can be compared against that stored in the image. Read-only and compressed images only.
You have double-clicked on a disk image, and macOS refuses. Here is what you can do to get that image to mount, even when it’s damaged.
An odd problem: you try running an old installer and it crashes. There’s nothing actually wrong with the installer, it’s just that the rules have changed.
How can you install older drivers or other software on a new Sierra system? Some practical tips for working through SIP and security protection.
Why do I see several disk images in the sidebar of Disk Utility?
How secure is an encrypted disk image that I might create using Disk Utility on my Mac?
Is there a way to lock an individual folder, so that it can only be opened on entry of a pre-set password?
Just when most software had settled on using Apple’s Installer, along came the App Store to add to complexity. And then there’s Adobe with its own downloaders and installers again. So how should we install and update software?
Disk Utility may seem the most mundane of all the utilities, but together with its command shell partners packs a real punch in several important areas.
The Eclectic Light Company 