Mac Dock icons rearranged themselves

Work out which one you have

Before changing anything, look at what actually moved. The fix depends on it.

1. New icons appeared on the right and pushed everything along

That is the recent apps section, not a rearrangement. Nothing you placed has moved; a temporary group grew beside it. Turn it off in System Settings › Desktop & Dock, or see how to stop recent and suggested apps.

2. Everything is in the same order but a different size or position

The Dock was resized or moved, most often by a brush of the divider or by connecting a display. The order is intact. See why the Dock keeps changing size and why it changes when you connect a monitor.

3. Your icons are genuinely in a different order

Something dragged them, and on a Mac only three things realistically do: a person, a trackpad misread as a drag, or an installer adding itself. macOS does not reorder pinned icons on its own.

An accidental drag is more common than people expect, because a slow drag on a trackpad reads as a deliberate one. System Settings › Accessibility › Pointer Control › Trackpad Options, and the dragging style there, is worth checking if it keeps happening.

4. The Dock came back as it was when the Mac was new

That is a reset, not a rearrangement, and it usually follows an update or a preference file being rebuilt. See why the Dock resets itself.

Stopping it, whichever it was

The contents lock stops the Dock's contents changing at all: no dragging out, no reordering, no new icons added. It is one setting and it covers cases one, three and four.

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

Set the Dock up the way you want it first. The lock freezes what is there, so locking a Dock you have not tidied preserves the mess. To release it, swap true for false.

If the size or position is also drifting, the other three locks are documented in three ways to lock the Mac Dock, and our free command generator writes whichever combination you want with the undo commands alongside.

After an update specifically

A macOS upgrade is the single most common trigger, and it is worth knowing why: an upgrade can rebuild com.apple.dock from defaults, which discards preferences that were never explicitly written. Anything you set once in a settings pane years ago is the most likely to vanish.

Values written from Terminal or delivered by a configuration profile survive, which is the real argument for setting them deliberately rather than clicking once and hoping.

Does locking the contents stop me installing apps?

No. Apps install normally and appear in Launchpad and the Applications folder. The lock stops them being added to the Dock, and stops icons being dragged out of it.

My Dock reordered itself after I connected a monitor.

Check the order carefully. Connecting a display usually resizes rather than reorders, and a Dock with smaller icons reads as a different Dock at a glance. See the monitor guide.

Will this survive a restart?

Yes. contents-immutable is written to your preferences and applies at every login. It is per user, so on a shared Mac each account needs it, or a configuration profile for all of them.

If you would rather not keep a list of commands, Still Dock is the same four settings as switches, and it remembers the Dock you had before you locked it. The size lock is free.