backupd

The first backup to a new disk copies everything and can take a long time. Later backups copy only what changed, but they can still be large after a macOS update, after moving big folders, or when a large file such as a virtual machine image or disk image changes.

Network backups to another Mac or network storage can take longer than backups to a directly connected disk.

In System Settings, General, Time Machine, click Options to exclude folders you do not need backed up, such as build output or caches that can be recreated. You can also skip a backup in progress from the Time Machine menu.

Do not quit backupd in Activity Monitor to stop a backup. Use Time Machine's own controls so the backup is stopped cleanly.

The Time Machine menu in the menu bar shows progress while a backup runs. Terminal gives the same answer in text.

If you disconnect the backup disk in the middle of the day, nothing is lost. Apple notes that Time Machine resumes its backup schedule when you reconnect the disk, so expect backupd to get busy again shortly after you plug it back in.

1. Run tmutil currentphase in Terminal. It prints the current step of the backup, or BackupNotRunning when nothing is happening.
2. Run tmutil status for more detail. Running = 1 means a backup is in progress and Running = 0 means it is not. While a backup runs, the output also includes its progress.
3. In Activity Monitor, click the Disk tab and find backupd and backupd-helper. Their Bytes Read count grows while files are being copied.

Apple lists a few causes, and they match what you see in Activity Monitor when backupd stays busy for a long time.

• Apps that store data in very large files and update them often. Time Machine backs up the whole file each time it changes.
• Antivirus or other utilities that keep the backup disk busy by scanning it. Apple suggests using the backup disk only for Time Machine.
• Backing up over a network, where speed depends on the network. A directly connected disk is faster.
• A lot of data on the Mac, which makes the preparing stage take longer.
• A backup disk that is not formatted as APFS on macOS Big Sur or later.

You can change the schedule instead of stopping backups altogether. On macOS Ventura and later, choose Open Time Machine Settings from the Time Machine menu, click Options, and pick a setting from the Back up frequency menu. The same Options window is where you exclude folders.

To check whether a folder is already excluded, run tmutil isexcluded ~/path/to/folder in Terminal. It prints [Excluded] or [Included] before the path.

Time Machine also makes local snapshots. Apple says these are created hourly, stored on the same disk as your files, and kept for up to 24 hours or until the space is needed. That is why you can see backupd activity on a laptop that is away from its backup disk.

To list the local snapshots on your startup disk, run tmutil listlocalsnapshots / in Terminal. It only reads the list and changes nothing.