Bytetallysyncdefaultsd — the process that keeps your app settings the same everywhere
Last updated: 2026-07-30
syncdefaultsd syncs small key-value data through iCloud — app preferences, toggle states, the little settings that follow you between your Mac and your iPhone. It appears often and moves almost nothing. In practice it is one of the least interesting processes on your Mac, and that is exactly what you want from it.
What it is
syncdefaultsd is the daemon behind iCloud's key-value store — the mechanism apps use to keep small pieces of state consistent across your devices.
The name is a clue if you know macOS internals. Application preferences on a Mac are stored in what the system calls *defaults*, and this process syncs them. When you toggle a setting in an app on your Mac and find it already toggled when you open the same app on your iPhone, this is what carried it.
It is deliberately not for content. Apple caps the key-value store at a small size precisely so developers use it for settings and not for data, which is what cloudd and bird are for.
Why it talks to the network
Three reasons, all of them small.
You changed a setting in an app that syncs preferences. The change is pushed up as a handful of key-value pairs.
Another device changed a setting, and the change comes down to your Mac. This is why it is active on machines you have not touched.
Periodic reconciliation, in which it confirms that both sides hold the same values. Because the data is so small, checking is cheap enough to do routinely.
The result is a process that appears frequently in any connection-level view and essentially never in a bandwidth-ranked one.
How much traffic is normal
Extremely small — this is one of the genuinely trivial processes on macOS.
A settings change is a few hundred bytes. A day of ordinary use might total a few hundred kilobytes, and even that is generous. The key-value store's size limit means there is a hard ceiling on how much it *can* legitimately move, which is unusual and useful: for most processes you cannot say what the maximum ought to be, but for this one you can.
That makes any large figure meaningful. If syncdefaultsd is showing megabytes, it is not syncing more settings than usual — something is failing and retrying. Rare, but worth noticing.
Can you turn it off
There is no dedicated switch, and no real reason to want one. This is a minor process: too small to be worth managing.
You could indirectly silence it by turning off iCloud for the apps that sync preferences, but doing that to save bandwidth would be trading a real feature for an unmeasurable gain. Killing the daemon accomplishes nothing durable, as launchd restarts it.
The honest advice is to leave it alone. On a list of things worth optimising on a Mac, syncdefaultsd is close to last — and knowing that a process is *not* worth your attention is a useful result in itself.
Seeing what it actually used
The value in measuring a process like this is negative confirmation: proving it is not the problem, so you can stop looking at it and go find what is.
Bytetally shows upload and download per process, so syncdefaultsd's row settles the question immediately — it sits at the bottom of the list where it belongs. And because it has a natural ceiling, it is one of the few processes where an unusual number is genuinely informative rather than just alarming.
Related processes
Common questions
What does syncdefaultsd actually sync?
Small key-value pairs, not files. This is the mechanism apps use when they want a setting to follow you — a preference toggled on your Mac appearing already toggled on your iPhone. The storage is deliberately limited in size, so it is used for settings rather than content.
Why does it run when I am not changing settings?
Changes from your other devices arrive through it too, and it performs periodic reconciliation to confirm both sides agree. Since each check is a handful of bytes, this happens often without amounting to anything measurable.
Can I disable syncdefaultsd?
There is no dedicated switch, and there is little reason to look for one — it is among the cheapest processes on the system. If you want it to have nothing to do, that follows from turning off iCloud for the apps in question, but doing so for bandwidth reasons would be pointless.
Should I worry if syncdefaultsd uses a lot of data?
Yes, because it should not be possible. The key-value store it uses is capped at a small size, so a large figure here means something is retrying in a loop rather than transferring legitimately. It is rare, but it is one of the few processes where any significant number is a signal.
See exactly how much it used
Bytetally tracks every process on your Mac separately — upload and download, live and historical. All on-device.
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