Why is backupd using so much CPU on my Mac?

What backupd is

Type man backupd in Terminal for Apple’s description: the Time Machine backup daemon, responsible for creating Time Machine backups and managing backup history. The page says there’s nothing to configure in it apart from exclusions, and that you shouldn’t run it yourself. A second process, backupd-helper, decides when to start backups (man backupd-helper).

Apple says that once Time Machine is on, it backs up automatically: hourly backups for the past 24 hours, daily backups for the past month and weekly backups for earlier months, deleting the oldest when the backup disk fills. It backs up your apps, music, photos and documents, but not the system files and apps that come with macOS.

The one-minute check

1. Click the Time Machine icon in the menu bar. Apple says it shows how much of the current backup is done, or the date and time of the latest one. No icon? Open System Settings, Control Center, scroll to Time Machine and choose Show in Menu Bar.
2. If it says it’s preparing, Time Machine is comparing your files with the last backup; Apple says it shows a Found message with the number of changes as it goes.
3. In Activity Monitor (Applications, Utilities), click CPU and type backup in the search field. backupd near the top while the menu shows a backup in progress is the backup at work.

Common causes, and what to do

The first backup

Apple says your first Time Machine backup includes everything on your Mac, that it can take longer than you expect, and that you can keep using the Mac while it runs. After that, Time Machine saves only new and changed items, so backups get smaller and faster.

What to do: Apple suggests setting up Time Machine in the evening so the first backup runs overnight. Leave the Mac awake and plugged in, with the backup disk connected.

A long preparing stage

Apple says preparing takes longer when the last backup was interrupted, the Mac wasn’t shut down properly, a disk was disconnected without being ejected, a software update was just installed, or the Mac went several days without a backup, for example because the backup disk was unplugged. How long it takes depends on how much is on the Mac, the size of the backup and the speed of the connection to the backup disk.

What to do: let it finish. Eject the backup disk before you unplug it next time, so the following backup doesn’t start with a long comparison.

Large files that change all the time

Apple says some apps keep their data in very large files that they change often, and Time Machine backs up the whole file each time it changes.

What to do: exclude them. Choose Apple menu, System Settings, General, Time Machine, click Options, add the file or folder to the list and click Save. Excluded items aren’t backed up at all, so only exclude what you can get back another way.

A network backup disk, or a slow connection

Over a network, Apple says backup speed depends on the network, and a disk connected straight to the Mac may be faster. For a USB backup disk, Apple says to check that the disk supports USB 3 and is plugged into a USB 3 port. Antivirus apps can slow backups badly; Apple suggests excluding the backup disk from their scans.

The Mac is busy, hot or low on battery

Apple says Time Machine is designed not to get in the way: it slows down when the Mac is busy or hot, or a laptop’s battery is low, and speeds up again once it’s idle, cool or charged. On a laptop, Options in Time Machine settings also has Back up on battery power, which lets the hourly backups run on battery.

What not to do

• Don’t force quit backupd. If you need the Mac’s full attention, click the Time Machine icon and choose Stop This Backup. Choose Back Up Now later to pick it up again.
• Don’t unplug the backup disk mid-backup. Apple says to eject it or shut down the Mac first. An interrupted backup makes the next one start with a longer preparing stage.
• Don’t worry about local snapshots filling your disk. Apple says Time Machine keeps hourly snapshots for 24 hours only on disks with plenty of free space, and that your Mac counts their space as available. See Why is my Mac storage full?

Keep an eye on it from the menu bar

The Time Machine icon shows the backup’s progress when you click it. Multimeter keeps the totals in the menu bar all the time:

• CPU: total use across all cores, every 3 seconds on power and about every 6 on battery. Yellow above 70%, red above 90% by default.
• Network speed: total upload or download per second across Wi-Fi and Ethernet, one direction per meter. Backing up to a network disk shows up as a steady upload; a USB disk doesn’t touch the network.
• Thermal pressure: Nominal, Fair, Serious or Critical, the state macOS uses to decide when to hold performance back. Apple says Time Machine slows down while the Mac is hot, so a backup takes longer then.
• Disk space: how full the startup disk is. It counts space macOS can free on its own as free, like Finder, so local snapshots don’t make it jump.

Multimeter’s built-in meters show totals for the whole Mac, not processes, so they won’t say the CPU is backupd. If you want the name too, the Busiest process recipe is a Script meter that shows the top process name and its % CPU. Five live meters use about 3% CPU, and they pause while the displays sleep.