What is nsurlsessiond on Mac, and why is it so busy?

What nsurlsessiond does

Its manual page (man nsurlsessiond in Terminal) describes it as "a per-user daemon that performs tasks for background-configured NSURLSessions", and adds that users "should not run nsurlsessiond manually". NSURLSession, now usually called URLSession, is the system apps use to download and upload over the internet.

When an app asks for a background session, the app doesn't do the transfer itself. Apple's developer documentation says "the actual transfer is performed by a process that is separate from your app's process", and that these tasks "continue to run even when your app is suspended" (Apple Developer, Downloading files in the background). That separate process is nsurlsessiond; an Apple engineer on Apple's developer forums calls it "the daemon responsible for handling NSURLSession background sessions" (Apple Developer Forums).

So Activity Monitor shows the network use, and some of the CPU and energy, under nsurlsessiond's name rather than the name of the app that asked for it. That's why it seems to appear from nowhere.

On our MacBook Pro with macOS 27.0.1, ps showed two copies: one running in our own account, and one running as a system account called _nsurlsessiond. Both are normal.

Why it gets busy

Because an app asked it to move data. Apple doesn't publish which of its own apps and services use background sessions, so you work out which one it is from the circumstances (next section). It's most likely to be busy:

• After you set up a new Mac or sign in to iCloud, when apps start bringing their data down.
• While apps download large items in the background, such as updates or media saved for offline use.
• When apps sync in the background, including third-party apps built on Apple's background transfers.
• Transfers that waited for better conditions. Apps can mark transfers as discretionary, and Apple says the system then "might delay transferring large files until the device is plugged in and connected to the network via Wi-Fi" (Apple Developer, isDiscretionary). That's why activity can start the moment you plug in or join your home network.

What's normal: bursts of network activity that end when a download finishes, with little CPU. Worth a look: heavy network use for hours that you can't connect to anything, or high CPU from nsurlsessiond itself for a long time.

How to find out what it's downloading

macOS doesn't show a list of who asked nsurlsessiond for what. Its log doesn't help much either: on our Mac, log show printed the client as <private>. So work from the evidence:

1. Measure it. In Activity Monitor, click Network and sort by Rcvd Bytes or Sent Bytes. A large and rising figure for nsurlsessiond confirms it's moving real data; the direction tells you whether it's mostly downloading or uploading.
2. Check iCloud Photos. In Photos, select Library in the sidebar, click All Photos and scroll to the bottom: the status there says whether it's uploading or downloading (Apple, Set up and use iCloud Photos).
3. Check iCloud Drive. In Finder, a small pie chart next to iCloud Drive in the sidebar shows transfers in progress; hold the pointer over it for the status (Apple, Check your iCloud Drive file and folder status).
4. Check the App Store and media apps for updates or downloads in progress.
5. Think about timing. Did it start after you signed in to iCloud, restored from a backup, turned on a sync feature or installed an app? That's usually the answer.

cloudd: the iCloud process you'll see next to it

If nsurlsessiond is busy, cloudd is often nearby. Its manual page calls it "the system daemon backing the CloudKit feature", the service many apps use to store and sync data in iCloud; it also says users should not run it manually. The Mac developer and writer Howard Oakley describes cloudd and bird as "the services for CloudKit and iCloud Drive respectively" (Eclectic Light). Together they're a sign of iCloud syncing; when it's files in iCloud Drive or a cloud storage app, see What is fileproviderd?.

Is nsurlsessiond safe?

Yes. It's part of macOS, stored at /usr/libexec/nsurlsessiond on the read-only system volume. To confirm the copy you see is Apple's, run this read-only command:

codesign -dv --verbose=2 /usr/libexec/nsurlsessiond

On our Mac it printed Identifier=com.apple.nsurlsessiond and Authority=macOS Software Signing. The same applies to cloudd, which lives inside a system framework. The data it moves is whatever your apps asked for, so if you're worried about an app, that's the app to look at, not nsurlsessiond.

How to calm it down

• Let it finish. Leave the Mac plugged in, awake and on Wi-Fi for a while. For iCloud Photos, Apple says the first upload "can take a while" and depends on the size of your library and your internet speed (Apple).
• Pause iCloud Photos for a day, if that's what is syncing. In Photos › Library › All Photos, scroll down and click Pause. Apple notes pause might not be available, depending on the library's status (Apple).
• Use Low data mode on a hotspot or metered network. Choose Apple menu › System Settings › Wi-Fi, click Details next to the network and turn on Low data mode, which Apple says reduces your data usage over that network; the steps are the same on macOS 15, 26 and 27 (Apple, Wi-Fi settings on Mac). Apple's iCloud Photos page notes that syncing can pause in Low Data Mode (Apple).
• Pause or limit the app responsible. If it's a sync or media app, its own settings usually have a pause or a "download over Wi-Fi only" option.
• Restart if a transfer seems stuck for hours, then check the app that started it.

What not to do

• Don't force quit it again and again. macOS starts it again when an app needs a transfer, so the download carries on or starts over; nothing is saved.
• Don't delete its folders, such as ~/Library/com.apple.nsurlsessiond, which its launch settings use to queue work. Removing them can lose queued transfers for your apps.
• Don't block it with a firewall app. Blocking nsurlsessiond blocks every app that relies on it, including iCloud features and app updates.

If the Mac is slow and nsurlsessiond isn't the cause, Why is my Mac so slow? goes through the others; photo analysis (mediaanalysisd) also runs after you turn on iCloud Photos, so the two can be busy at the same time. For reading the Network tab in more detail, see Activity Monitor on Mac.

How Tend helps

Tend's free Energy & Apps page can show it: choose Everything instead of Apps, and the copy of nsurlsessiond that runs in your account appears with its CPU and estimated watts. Like any app without administrator rights, Tend can't see the copy macOS runs under its own account. The Energy over time card ranks what used the most energy over the last 24 hours (7 and 30 days with Pro), as a total for the period: if the copies of nsurlsessiond and cloudd in your account were among the biggest users, they're listed there next to your apps. It counts only time the Mac was awake, and the figures are estimates.

Questions

Related guides

Sources

• Apple, man nsurlsessiond and man cloudd on macOS 27.0.1
• Apple Developer, Downloading files in the background and isDiscretionary
• Apple Developer Forums, reply from Apple Developer Technical Support on background sessions
• Apple, Set up and use iCloud Photos
• Apple, Use iCloud Photos on Mac
• Apple, If your iCloud Photos aren't syncing or syncing with iCloud is paused
• Apple, Check your iCloud Drive file and folder status on Mac
• Apple, Wi-Fi settings on Mac
• Howard Oakley, Eclectic Light, How does iCloud work? (independent, not Apple)

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