Electron-Builder Version

26.4.0

Target

macOS (arm64)

Description

DMG builds fail on macOS 26.4 Tahoe (beta) with the error "Unable to attach disk image" followed by "hdiutil: attach failed - no mountable file systems".
This is caused by a known issue in the macOS Tahoe beta affecting HFS+ mounting. Apple has acknowledged this in their official release
notes:

From macOS Tahoe 26.4 Beta Release
Notes:

"External Media - Known Issues: HFS external media might fail to mount automatically. (168672160)"
The dmgbuild library bundled in dmg-builder defaults to creating HFS+ sparse images, which triggers this bug.

Error Output

⨯ /usr/bin/python3 process failed 1
Exit code: 1
dmgbuild.core.DMGError: Unable to attach disk image:
hdiutil: attach failed - no mountable file systems

Root Cause Analysis

The DMG build process in dmgbuild/core.py:

1. Creates a writable HFS+ sparse image
2. Attaches the sparse image via hdiutil attach ← fails on macOS Tahoe beta
3. Populates the mounted volume
4. Detaches and converts to read-only DMG
   Verification:

HFS+ sparse image - FAILS on macOS 26 Tahoe

hdiutil create -size 200m -fs HFS+ -volname "Test" -type SPARSE /tmp/test_hfs.sparseimage
hdiutil attach -nobrowse -owners off /tmp/test_hfs.sparseimage

Error: hdiutil: attach failed - no mountable file systems

APFS sparse image - WORKS

hdiutil create -size 200m -fs APFS -volname "Test" -type SPARSE /tmp/test_apfs.sparseimage
hdiutil attach -nobrowse -owners off /tmp/test_apfs.sparseimage

Proposed Fix

Change the default filesystem from HFS+ to APFS in dmg-builder/vendor/dmgbuild/core.py.

Why APFS is the better default

• Future-proof: Apple has been moving away from HFS+ since 2017. All new Macs ship with APFS.
• Better performance: APFS is optimized for modern storage (SSDs, NVMe) which all Apple Silicon Macs use.
• Wide compatibility: macOS 10.13+ covers 8+ years of macOS releases (2017-2025), which is sufficient for most Electron app
  deployment targets.
• Avoids beta bugs: Works around the current macOS Tahoe beta issue and any future HFS+ deprecation Apple may implement.
• No user impact: The filesystem is only used during the build process for the temporary sparse image - the final DMG output format
  remains unchanged. Electron itself has minimum macOS requirements - Electron 22+ requires macOS 10.13+, so your users already need High Sierra or later

Environment

• macOS: 26.4 Tahoe (beta)
• Architecture: Apple Silicon (arm64)
• electron-builder: 26.4.0
• dmg-builder: 26.4.0

Related Issues

• Issue with hdiutil when building on MacOS  #8415 - hdiutil issues (different error - hdiutil convert)
• Universal build fails on non-ARM64 hardware, and M1 target DMG is 'damaged' #5850 - M1 deprecating HFS+
• Operation not permitted during dmg building on macOS 11 Big Sur #5465 - HFS+ issues on Big Sur