balenaEtcher Stuck at Starting on macOS: Erase the USB Drive as exFAT

$ diskutil list
$ diskutil unmountDisk force /dev/diskN
$ diskutil eraseDisk ExFAT USB GPT /dev/diskN

I wanted to repurpose my old Mac, a 2011 iMac, by putting Linux Mint on it. I wrote the installer USB drive on my Apple Silicon MacBook Pro with balenaEtcher. Etcher stopped at “Starting…” and gave no reason, so I wrote the drive with dd, and the iMac booted from it. Later I reproduced the hang on a second drive to find the cause.

Symptoms

balenaEtcher (also searched as Balena Etcher) detects the drive and loads the ISO. After you click Flash, the window stays at:

Starting...

No progress bar appears and no error is raised. Launching the app from a terminal with elevated permissions makes no difference:

sudo /Applications/balenaEtcher.app/Contents/MacOS/balenaEtcher

Etcher’s DevTools console shows the flasher starting and then stopping short of the write. This is Etcher 2.1.6 with an APFS-formatted drive:

Starting priviledged flasher sidecar on port 3435
/Applications/balenaEtcher.app/Contents/Resources/etcher-util
... with privileges ...
elevated pending
...
elevated granted
etcher-<id>
Connection to sidecar flasher process attempt 1 / 10 failed; retrying in 1000ms...
etcher-<id>
CHILD READY
start heartbeat
params Object
CHILD LOG: Ready ...
CHILD LOG: write requested
CHILD LOG: Image: /Users/<user>/Downloads/<image>.iso
CHILD LOG: Devices: /dev/diskN
CHILD LOG: Auto blockmapping: true
CHILD LOG: Decompress first: true

The log reaches write requested, echoes the job’s settings, and no bytes follow. In the log, <user> is your account name and <image> is the ISO you selected. N is your drive’s disk number, and <id> is a random name Etcher gives each helper run.

APFS drive that stops the helper before the write

Etcher doesn’t write the disk itself. The Electron app launches a separate privileged helper, the “sidecar flasher”, and hands it the image and the device. The CHILD LOG lines after write requested are the helper echoing that request back. Etcher asks macOS for administrator rights for the helper itself, which is what the elevated pending and elevated granted lines record, so sudo adds nothing. Run as sudo, the log is identical.

The log doesn’t show why the helper stops. The drive’s format does. I reproduced the hang with a second USB drive, a different ISO and Etcher 2.1.6, and changed only the format between two runs:

Erased as exFAT, the same flash continued straight into progress:

CHILD LOG: Decompress first: true
Flashing 1 device, 0% at 1.60 MB/s (total 1.60 MB/s) eta in 235s with 0 failed devices

That matches the reports on balena’s forums. One thread (opens in a new tab) states that Etcher doesn’t work on an APFS drive and surfaces no error. Another (opens in a new tab) with this hang was resolved by erasing the drive as exFAT.

A USB drive isn’t APFS unless someone made it so. Disk Utility offers APFS only when you erase the whole device with a GUID partition map, not when you erase a volume on a drive with the older MBR layout. I don’t know what the first drive was formatted as when it hung. dd wrote the Mint image to it without an error, so the ISO and the drive weren’t at fault.

Erase the USB drive as exFAT

The erase replaces the drive’s partition map and every volume on it. Copy off anything you need from the drive first.

1. Find the USB drive

$ diskutil list

Find the header that reads external, physical and matches your drive’s size. Its number replaces N in the next step. An APFS drive also appears a second time, as a synthesized container. Use the external, physical identifier, not the container’s.

2. Erase it

$ diskutil unmountDisk force /dev/diskN
$ diskutil eraseDisk ExFAT USB GPT /dev/diskN

force matters when Spotlight is indexing the drive. Without it, the erase can fail with Couldn't unmount disk. : (-69888) and name the process mds. USB is the new volume name; any name works, because the flash overwrites it.

3. Flash again

Select the ISO and the drive in Etcher, and click Flash. Within a few seconds, the window shows Flashing... with a percentage, and the DevTools log shows Flashing 1 device lines.

Write the ISO with dd instead

If Etcher still stops after the erase, dd writes the image without Etcher’s helper. That’s how the Mint drive in this article was written. The steps, the checks that keep dd off the wrong disk, and how to confirm the write are in Create a bootable Linux USB drive on macOS with dd.