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macOS ships with a powerful set of built-in tools that most engineers barely scratch the surface of. Whether you need to roll back to an older release for compatibility testing, clear a stubborn DNS cache, or just shave seconds off repetitive workflows, this page collects the day-to-day tricks that actually matter on a working machine.

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Installing or Downgrading macOS

Sometimes you need a specific macOS release — for virtual machine images, compatibility testing, or simply because a new feature broke your toolchain. Apple keeps older installers available through the Mac App Store; clicking any link below opens the store page directly on your Mac.
Mojave (10.14) or later is required to access these App Store links. On older systems you may need to use a bootable USB installer instead.
VersionNameApp Store Link
macOS 26Tahoe (latest)Use Software Update in System Settings
macOS 15SequoiaOpen in App Store
macOS 14SonomaOpen in App Store
macOS 13VenturaOpen in App Store
macOS 12MontereyOpen in App Store
macOS 11Big SurOpen in App Store
macOS 10.15CatalinaOpen in App Store
macOS 10.14MojaveOpen in App Store
macOS 10.13High SierraOpen in App Store
You can also check for the latest Tahoe upgrade from the terminal without opening System Settings: 
softwareupdate --list
softwareupdate --list shows all available system updates, including the Tahoe upgrade if your Mac is eligible. Once you see it listed, install it directly with softwareupdate --install <label>, or continue through System Settings → Software Update for the guided flow.

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Flushing the DNS Cache

When DNS changes aren’t reflecting — after editing /etc/hosts, switching VPNs, or pushing a new DNS record — flushing the local resolver cache is the fastest fix.
This command requires Administrator (sudo) privileges. You will be prompted for your password.
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
The two-part command first clears dscacheutil’s cache store, then sends mDNSResponder a hang-up signal so it reloads with an empty slate. No reboot required.

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Adding and Removing Dock Separators

Grouping Dock icons with invisible spacers keeps things organised without switching to a third-party launcher. There are two spacer styles:
Big Sur introduced a smaller, half-width spacer that is useful when you want a subtle visual break rather than a full icon-width gap.
defaults write com.apple.dock persistent-apps -array-add \
  '{tile-data={}; tile-type="spacer-tile";}' && killall Dock
Removing spacers — two options:
1

Drag and drop

Click and hold a spacer, then slowly drag it upward out of the Dock until a Remove label appears, then release. The Dock bounces and the spacer disappears.
2

Nuke all spacers at once

If the Dock is cluttered with leftover spacers, reset the persistent-apps array entirely. This removes all spacers but leaves your real app icons intact on the next login.
defaults delete com.apple.dock persistent-apps && killall Dock
This command resets the entire persistent-apps list to the macOS default. Back up your current Dock layout first if you have a carefully tuned setup.

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System Settings Shortcuts

Navigating deep into System Settings by hand is slow. These URL schemes open specific panes directly — paste them into Spotlight or run with open: 
open "x-apple.systempreferences:com.apple.Network-Settings.extension"
You can also jump to any System Settings pane by typing its name directly into Spotlight (⌘ Space). Type “DNS” or “VPN” and the relevant Network pane appears as the top result.

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Spotlight Tips

Spotlight (⌘ Space) is more than a file launcher — it doubles as a quick calculator, unit converter, dictionary, and system-settings shortcut.
What to typeWhat you get
42 * 1.21Inline calculator result
100 USD in EURLive currency conversion
define resilientDictionary definition inline
App or pane nameDirect launch / Settings pane
~Home directory in Finder
File extension, e.g. .tfAll matching files on disk
If Spotlight results feel stale, re-index with:
sudo mdutil -E /
This forces a full re-index of the boot volume. Expect higher CPU usage for a few minutes while the index rebuilds.

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Screenshot Shortcuts

macOS has a built-in, fully-featured screenshot toolkit — no third-party tool needed for most workflows.
ShortcutAction
⌘ Shift 3Capture full screen to Desktop
⌘ Shift 4Crosshair — drag to capture a region
⌘ Shift 4, then SpaceClick a window to capture just that window (with shadow)
⌘ Shift 5Screenshot toolbar — region, window, screen recording
⌘ Shift 6Capture the Touch Bar (if present)
Add Control to any shortcut above to copy to clipboard instead of saving to a file. For example, ⌘ Shift Control 4 lets you drag a region and paste it straight into Slack or a ticket.
Change the default save location, file format (PNG/JPG), and whether shadows are included by opening the Screenshot toolbar with ⌘ Shift 5 and clicking Options.

macOS Terminal

Homebrew, Zsh customisation, SSH key management, and DevOps-friendly aliases for the command line.

Linux Essentials

Core commands and concepts that transfer directly between Linux and macOS terminal sessions.

Linux Networking

Deeper networking diagnostics — useful when DNS flushing alone doesn’t solve the problem.

Linux Troubleshooting

Systematic debugging patterns applicable to both Linux servers and macOS development machines.
Last modified on June 9, 2026