“zsh: permission denied” on macOS: The Three Causes and Their Fixes
zsh: permission denied looks like one error, and it is really three. The shell says it when a file has no execute bit, when the thing you pointed at cannot be executed at all, and…
“Disk Not Ejected Properly” on Mac: What Causes It and How to Eject Safely
The “Disk Not Ejected Properly” notification appears after the fact: a volume that macOS still had mounted is suddenly gone. Pulling a cable is the obvious way to cause it, but it also shows up…
Finder Not Responding on Mac: How to Relaunch It and Find the Cause
Finder stops redrawing, the spinning wheel appears, and clicking a window does nothing. Relaunching Finder is the standard first move, and it is safer than force quitting a regular app: Finder is managed by launchd,…
How to Check an App’s Code Signature on a Mac with codesign
When you download an app outside the App Store, codesign is the built-in way to check who actually signed it and whether the copy on disk has been tampered with. It reads the signature that…
How to Use netcat (nc) on a Mac to Test Ports
Every Mac already has nc — netcat — so there is nothing to install to check whether a port is open, scan a short range, or stand up a throwaway listener to test a connection.…
How to Use osascript: Run AppleScript from the Mac Terminal
The osascript command runs AppleScript — and JavaScript — straight from the Terminal, which makes it the bridge between a shell script and the Mac’s GUI layer. It is how a shell script pops a…
How to Zip Files on a Mac Without the __MACOSX Junk
There are two easy ways to make a zip on a Mac: right-click a folder in the Finder and choose Compress, or run zip in the Terminal. Both work. The problem shows up on the…
The sips Command: Convert and Resize Images from the Mac Terminal
Every Mac ships with sips — Scriptable Image Processing System — so there is nothing to install to convert, resize, or rotate an image from the Terminal. For a single photo, the Finder is honestly…
How to Use crontab on macOS (and Why Cron Jobs Don’t Run)
cron still works on macOS. The crontab command is built in — there is nothing to install — and it schedules jobs with the same five-field syntax you would use on Linux. The trouble Mac…
How to Use rsync on macOS: Examples and Common Flags
rsync copies and syncs folders efficiently — it only transfers the parts that changed, which makes it ideal for backups and for keeping two machines in step. It’s built into macOS, so there’s nothing to…