The Dock settings Apple never gave you a switch for

The four that work

Each is a single line in Terminal. Open Terminal from Applications then Utilities, paste a line, press Return.

Lock the size

The divider stops responding, and the size slider in System Settings greys out.

defaults write com.apple.dock size-immutable -bool true; killall Dock

Lock the position

The Dock stays on the edge you chose. Bottom, left or right.

defaults write com.apple.dock position-immutable -bool true; killall Dock

Lock the contents

Apps can no longer be dragged out, dropped in, or rearranged. Useful on a shared or family Mac, where the usual complaint is an app that has silently vanished from the Dock.

defaults write com.apple.dock contents-immutable -bool true; killall Dock

Lock hide and show

Pins the auto-hide setting so it cannot be flipped, by accident or by another app. This one is rarely documented.

defaults write com.apple.dock autohide-immutable -bool true; killall Dock

Undoing any of them

Run the same line with false in place of true:

defaults write com.apple.dock size-immutable -bool false; killall Dock

To clear all four at once, and nothing else:

defaults delete com.apple.dock size-immutable
defaults delete com.apple.dock position-immutable
defaults delete com.apple.dock contents-immutable
defaults delete com.apple.dock autohide-immutable
killall Dock

The one that does not work

You will find magnification-immutable repeated across forums and listicles as a fifth lock. We tested it on macOS 26. It does nothing. The setting is written, no error appears, and magnification remains fully adjustable in System Settings.

If you want magnification held steady, there is no preference for it. Turn it off instead.

Things to know before you rely on this

• killall Dock is not optional. Writing the preference on its own greys out the control in System Settings but the Dock keeps letting you resize it until it restarts. Nearly every guide that leaves this out produces a lock that appears to fail.
• The lock freezes what is current. Set the Dock exactly how you want it first. There is no way to specify a size in the command.
• System Settings gives you no explanation. The Dock controls grey out and macOS says the setting has been configured by a profile. There is nothing to indicate that it was you, months ago, in Terminal.
• Nothing is remembered. There is no record of the Dock you had before locking. Unlock, and you are back to dragging the divider by hand.
• It is per user account. Other accounts on the same Mac are unaffected, and each needs the commands run separately.
• Managed Macs may override you. On a work or school Mac an actual configuration profile can enforce Dock settings, and that wins over anything you set locally.

Checking what is currently set

To see whether a lock is on:

defaults read com.apple.dock size-immutable

1 means locked, 0 means unlocked, and an error saying the key does not exist means it was never set.

When the commands are enough, and when they are not

If you set your Dock once and never change it, run the commands and you are done. They cost nothing and they hold.

They start to grate when your Dock is something you actually adjust. Every change means finding the commands again, unlocking, adjusting, relocking. There is no record of what you had, so a lock applied at the wrong moment freezes the wrong size permanently. And none of it follows you to a new Mac.

Locking the Dock with Still Dock is these same four settings as four switches in the menu bar. It records the Dock you had before each lock and restores it when you unlock, quit, or delete the app, so nothing is ever stuck. You can try how it behaves in your browser first.

Using more than one screen? The Dock also jumps between them, which is a separate problem with its own fixes: how to keep the Mac Dock on one screen.

Common questions

Is this safe?

Yes. These are documented macOS preferences, the same ones IT departments use to standardise Macs. Nothing is patched or modified, and every one of them reverses with a single command.

Do I need admin rights?

No. These write to your own user preferences, so no password is required. That also means any user can undo them for their own account.

Will locking the Dock speed up my Mac?

No. These settings only prevent changes. They have no effect on performance.

Can I lock the Dock to one monitor?

Not with these. Which display shows the Dock is governed by Mission Control, not by these preferences. Turning off Displays have separate Spaces keeps the Dock on one screen, at the cost of per-display full screen apps.