error:"hdiutil: attach failed - Permission denied" , issue in installing cask on external drive

[Ayush-Mgr]

Verification

• I understand that if I ignore these instructions, my issue may be closed without review.
• I have retried my command with --force.
• I ran brew update-reset && brew update and retried my command.
• I ran brew doctor, fixed as many issues as possible and retried my command.
• I have checked the instructions for reporting bugs.
• I made doubly sure this is not a checksum does not match / SHA256 mismatch error (do not open an issue before trying to open a PR to fix first).

Description of issue

hdiutil: attach failed - Permission denied when installing casks on external drive

I'm encountering a permission error when attempting to install casks using Homebrew on an external drive. Specifically, the error occurs during the hdiutil attach process.

Steps to Reproduce:

1. Set Cask Installation Directory to External Drive:

   I configured Homebrew to install casks to an external drive by setting the HOMEBREW_CASK_OPTS environment variable:

   export HOMEBREW_CASK_OPTS="--appdir=/Volumes/disk_2/apps"

2. Verify Directory Permissions:

   Checked the permissions of the target directory:

   ls -ld /Volumes/disk_2/apps

   Output:

   drwxr-xr-x@ 29 yush  staff  986 Mar  6 16:59 /Volumes/disk_2/apps
   

3. Attempt to Install a Cask (e.g., Blender):

   Executed the following command:

   brew install --cask blender

   Encountered the following error:

   ==> Downloading https://formulae.brew.sh/api/cask.jws.json
   ==> Downloading https://raw.githubusercontent.com/Homebrew/homebrew-cask/507608b
   Already downloaded: /Users/yush/Library/Caches/Homebrew/downloads/d914cba5818691ff14efe8c1c80c5da1b857a0c6c49a5a3b6efb794d915a0a5a--blender.rb
   ==> Downloading https://download.blender.org/release/Blender4.3/blender-4.3.2-ma
   Already downloaded: /Users/yush/Library/Caches/Homebrew/downloads/3c619b9faa69ce1cd91337345e353c2a19036146f6082a0824bad3711275e4bd--blender-4.3.2-macos-arm64.dmg
   ==> Installing Cask blender
   hdiutil: attach failed - Permission denied
   ==> Purging files for version 4.3.2 of Cask blender
   Error: Failure while executing; `/usr/bin/env hdiutil attach -plist -nobrowse -readonly -mountrandom /Volumes/disk_2/apps/brew/temp/homebrew-dmg20250306-1279-myckox /Volumes/disk_2/apps/brew/temp/homebrew-dmg20250306-1279-myckox/3c619b9faa69ce1cd91337345e353c2a19036146f6082a0824bad3711275e4bd--blender-4.3.2-macos-arm64.cdr` exited with 1. Here's the output:
   hdiutil: attach failed - Permission denied
   

Additional Information:

• macOS Version: [Mac mini m4]
• Homebrew Version: [Homebrew 4.4.23]
• External Drive Format: [File system format of /Volumes/disk_2]

Troubleshooting Steps Taken:

Granted Full Disk Access to Terminal:

• Navigated to System Settings > Privacy & Security > Full Disk Access.
• Added the terminal application and restarted it.

Result: The error persists.

Request for Assistance:

I seek guidance on resolving the hdiutil: attach failed - Permission denied error when installing casks to an external drive using Homebrew. Any insights or recommendations would be greatly appreciated.

Command that failed

brew install --cask blender

Output of command with --verbose --debug

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Output of brew doctor and brew config

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Output of brew tap

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