Mac maintenance: flush DNS, rebuild Spotlight and fix "Open With"

For fixing problems, not for routine

A lot of Mac maintenance advice is folklore. Tidy My Mac's Maintenance section says it plainly at the top: run one of these when something is wrong, not as a routine, because none of them makes a healthy Mac faster.

That is also why some familiar tasks are missing. There is no "free up RAM" button, because macOS refills that cache straight away. There is no "repair disk permissions", which macOS dropped years ago, and no periodic maintenance scripts, which are gone from current macOS too.

The four tasks

How to flush the DNS cache on a Mac

Your Mac remembers the address behind each site name for a while. When a site moves to a new server, or you switch networks or VPNs, that memory can point to the wrong place, and the site won't load even though it works everywhere else. Flushing the cache makes your Mac look each name up again.

Flush DNS Cache does what the usual Terminal recipe does: it runs dscacheutil -flushcache and then tells mDNSResponder, the macOS service that answers DNS lookups, to drop its cache. Because that service runs as the system, macOS asks for an administrator password.

How to rebuild the Spotlight index

When Spotlight can't find a file you know is there, or keeps showing one you deleted, its index is out of step with the disk. Rebuild Spotlight Index erases the index of your startup disk with mdutil -E /, and macOS rebuilds it from scratch in the background. That can take from minutes to hours on a full disk, and search results are incomplete until it finishes, so it is best started when you won't need Spotlight for a while.

Fix duplicate apps in the "Open With" menu

The "Open With" menu and your default apps come from a macOS database of every app it has seen. Over time it collects old versions, copies on disk images and apps you deleted, so the menu fills with duplicates or files open in the wrong app. Rebuild "Open With" Menu runs Apple's lsregister tool to clean the database out and register your apps again. It runs as you and needs no password.

Clear font caches

macOS caches the fonts you have installed. A damaged cache shows up as garbled text, missing characters or the wrong font in apps. Clear Font Caches removes your user's font cache databases with atsutil, and macOS builds fresh ones. It needs no password; log out and back in for it to take effect.

One password for the batch

Select several tasks and run them together. The ones that need administrator rights run first, through a single macOS password prompt, so you aren't asked twice and you find out right away if you cancel. Your password goes to macOS's own prompt, not to Tidy My Mac.

Each task then shows when it last ran, or why it didn't finish. Finished tasks are also recorded in the Dashboard's Cleanup history, without Put Back, since nothing was moved to the Trash.

When the problem is speed

If your Mac is slow rather than broken, these tasks won't help. Look at Performance to see which app is busy or using memory, Startup Items for what starts at login, and Background Services for what keeps running.