Problem prevention
OS X will often alert you to upcoming problems, if you know where to look
will often advise keeping around 10% of your startup disk free for temporary storage. These days, that figure may seem a bit excessive now that drive capacities are far larger.
However, if you’re using an older computer, or a Mac with a small amount of memory, either add more memory or free up some storage to improve performance. Use Activity Monitor to check memory usage; if the Memory Pressure graph regularly shows orange or red, more memory will mean macOS doesn’t have to write the contents of memory used by idle apps out to disk in order to free up some for apps that need it.
On a Mac with a hard drive (not flash storage), keep at least the same amount of free storage as your Mac has memory, so the latter’s contents can be saved to disk if the Mac enters Safe Sleep when its battery runs low or it’s left idle for a long time.
You might want to think about upgrading to a faster hard drive, or even an SSD, for further gains – you’ll find visual guides for many Macs at ifixit.com.
Optim alperformance
macOS runs optimization scripts overnight if your Mac’s turned on or in sleep mode, but you can force them to run manually at any time by opening Terminal (in /Applications/Utilities) and typing: sudo periodic daily weekly
monthly (or any combination of the last three words), then pressing ® .
Though macOS is good at keeping things in order, apps can interfere with its settings, causing problems. Permissions define who can access, execute, write to or delete a file on disk, and are used to limit the damage that unauthorized users or routines can cause. It’s possible for an app to erroneously lock a file by changing its permissions, which could cause other apps to crash when they can’t access a required resource, such as the place where iTunes records play counts for tracks.
Up to OS X 10.10, open Disk Utility, select the startup disk, click the First Aid tab, then Repair Permissions. As of OS X 10.11, System Integrity Protection ( apple.co/29LWvsP) protects the permissions of important system files and apps, which are now checked and repaired automatically when you install system updates.
If your Mac’s running slow, you should be able to diagnose the problem using Activity Monitor (again, in the Utilities folder). If your Mac is hot or its fans are running at high speed, click the CPU tab, then the “% CPU” column header to sort processes by usage. Similarly, use the Disk tab to diagnose which app is thrashing storage, and Memory and Network to check general slowness or a slow internet connection. You can force an unresponsive app or a process hogging resource to quit, but do this with care: only quit those for which your own username appears in the User column, and save your work first, if possible, to minimize potential data loss.