How to Resume an Interrupted File Copy on a Mac

A copy to a NAS or an external drive stops halfway: the Wi-Fi drops, the cable gets nudged, the Mac goes to sleep. On a recent macOS, the Finder can often pick up where it stopped: look for the greyed-out item it left in the destination, Control-click it and choose Resume Copy. When that option isn't there, rsync in Terminal can continue the job without starting from zero. And if big copies to other disks are part of your week, a file manager that waits for the volume and resumes on its own saves you the babysitting.

Resume an interrupted copy in the Finder

Since macOS Monterey, a Finder copy that is cut short doesn't simply vanish. The file it was writing stays in the destination as a greyed-out item, and the Finder remembers how far it got.

1. Open the destination folder (on the NAS, the external drive or the other folder).
2. Find the greyed-out item with the same name as the one you were copying.
3. Control-click it (or right-click) and choose Resume Copy.

The copy continues from where it stopped instead of rewriting the whole file. If you would rather start over, delete the greyed-out item and copy again.

When the Finder can't resume

The option is not always offered, and it is worth knowing the usual cases:

• The destination disk was unplugged or the network share disconnected. Reconnect the share or the drive first (for a server, ⌘K in the Finder opens the connection window), then check whether the greyed-out item is still there. Sometimes it is gone, and the copy has to start again.
• You copied a whole folder. Resuming concerns the file that was cut; the files the Finder had not reached yet are not copied by it. Compare the two folders and copy only what is missing, or let rsync (below) work it out for you.
• The copy failed with an error rather than stopping. An error on one file can end the whole operation. Note which file it was, copy the rest, then deal with that file on its own.

The Finder doesn't wait for a server that stops answering: a short network drop can be enough to end a long copy with an error.

Resume a copy with rsync in Terminal

rsync compares the source and the destination and only sends what is missing or different. Running the same command again after an interruption therefore continues the copy:

rsync -ah --partial --progress ~/Movies/Project/ /Volumes/NAS/Project/

• -a keeps dates, permissions and folder structure; -h shows readable sizes.
• --partial keeps a half-copied file instead of deleting it, so a later run can reuse what was already sent.
• --progress shows each file as it goes.
• The slash at the end of the source (Project/) copies the contents of the folder into the destination folder.

If the connection drops, run exactly the same command again: complete files are skipped, and the copy moves on. The rsync that comes with macOS is an older or reduced version; if an option is refused, a current rsync from Homebrew (brew install rsync) accepts all of them.

To keep the Mac from going to sleep during a long transfer, put caffeinate -i in front of the command:

caffeinate -i rsync -ah --partial --progress ~/Movies/Project/ /Volumes/NAS/Project/

Make big copies survive interruptions with Folia Files

If you regularly move large folders to a NAS, a server or an external drive, Folia Files handles interruptions for you. Its copies go file by file, and when a volume stops answering in the middle, it waits for it instead of failing.

Copies that wait, then resume on their own

Open the source in one pane and the destination in the other, select what to copy and press F5 (File › Copy to Other Pane), or drag the items across. If the share or the disk disappears during the copy, the progress line in Operations says Waiting for “NAS”… the copy will resume on its own. Plug the disk back in or let the network come back, and the copy continues where it stopped:

• files already copied completely (same size and date) are recognised and left alone;
• large files (64 MB and more) copied to another disk are written in chunks and continue from the last bytes written, not from the beginning;
• a file in the destination that differs from the source and was not left by this copy is never overwritten: it is reported instead.

How long Folia Files waits is set in Settings › Files and Network › Copies: Wait for the volume up to goes from 30 seconds to 15 minutes (2 minutes by default).

Resume later, even after quitting

If the volume doesn't come back in time, the copy stops with a Copy Interrupted alert. What was already copied stays, and Resume continues from there whenever the disk or the server is available again. If Folia Files was quit or the Mac restarted in the middle of a copy, the next launch shows A Copy Wasn't Finished with the same Resume button (or Forget).

A file that can't be read is reported by name, and the rest of the copy goes on: one bad file no longer ends the whole operation.

Verify, stay awake, one copy at a time

The other settings of the Copies section help with long transfers:

• Verify every file copied to another disk (read back and compared, slower): each copy is read back and compared with its original; a copy that doesn't match is deleted and reported.
• Keep the Mac awake during copies, backups and imports: on by default. The screen can still turn off; a MacBook with its lid closed still goes to sleep.
• One copy at a time per destination disk (others wait their turn): two copies to the same NAS don't fight for its speed.
• Maximum speed to network volumes: leaves bandwidth for everything else during a big upload.

A server that stops answering doesn't freeze the app either: the rest of the window stays usable while the copy waits. These copies work the same way in the website version and the Mac App Store version.

Which method should you use?

• One big file, a single interruption: try the Finder's Resume Copy first.
• A whole folder, or the Finder can't resume: rsync -ah --partial and run it again until it finishes.
• Regular large copies to a NAS, a server or external drives: a copy that waits for the volume, resumes by itself and can verify each file — that is what Folia Files is built for.

If the drive refuses to eject once the copy is done, here is how to eject a disk that says it's in use. And to copy to SFTP or S3 without installing anything in the system, see how to connect to SFTP and S3 without macFUSE.