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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.
You can also check for the latest Tahoe upgrade from the terminal without opening System Settings:
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.
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.
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.
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:
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.
If Spotlight results feel stale, re-index with:
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. 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