An Automator workflow that mounts a disk image on when I drag and drop the dmg file onto it is easy: enter image description here

Instead of dragging and dropping the dmg file I want to double click the created workflow and have it mount a specific file. I've tried using "Set Value of Variable" to the path of the dmg, "Open Finder Items", and "Get Selected Folder Items", nothing works.

I can do it with the command line as:

hdiutil mount disk_image_name.dmg

I've also tried with the Applescript:

    on run {input, parameters}

        tell application "DiskImageMounter"
            open "path/disk_image_name.dmg"
        end tell
    end run

But after mounting the disk image as expected, Automator freezes for about 15 seconds and gives the below Syntax Error.

enter image description here

The reason I want to avoid using hdituil is the disk images are encrypted. When using the Automator mount tool the password is done in Apple's dialog box. Using hdiutil I end up passing the password as stdin.

printf '%s\0' "$PASSPHRASE" | hdiutil attach $LOCATION -stdinpass 
  • Is the some good reason you cannot just double click the target DMG file in Finder? That will prompt for the password and mount it if the proper password is given. Commented Dec 24, 2019 at 0:52
  • Don't use DiskImageMounter. This is one instance where you should use Finder as it is more reliable (which is the only time this is ever true).
    – CJK
    Commented Dec 24, 2019 at 1:04
  • @user3439894 I can't just double click because there is more to the workflow than just mounting the image.
    – OrigamiEye
    Commented Dec 24, 2019 at 8:26
  • @CJK I tried and Applescript with tell "Finder" but it cannot open dmg files.
    – OrigamiEye
    Commented Dec 24, 2019 at 8:26
  • @OrigamiEye I suggest to use hdiutil mount ... with a p12 but no password (cert based disk image protection with the keychain which requires a password only once). Takes ~3 minutes work in the shell and requires run shell script > hdiutil mount /path/to/disk_image_name.dmg in a workflow only
    – klanomath
    Commented Dec 24, 2019 at 13:57

2 Answers 2


I would use hdiutil ... instead of other methods but with an image protected by a certificate instead of a password. This is similar as to building an encrypted image with a password and a recovery key (based on a cert) - without password though:

  1. Create a temporary cert folder and cd into it:

    mkdir ~/certsecdmg
    cd ~/certsecdmg 
  2. Create a root CA if you don't have one already:

    openssl genrsa -des3 -out casecdmg.key 4096
    openssl req -new -x509 -days 7300 -key casecdmg.key -out casecdmg.crt

    Fill in all proposed fields.

  3. Create a password protected certificate signing request:

    openssl genrsa -des3 -out secdmgbuild.key 4096 
    openssl req -new -key secdmgbuild.key -out secdmgbuild.csr

    Fill in all proposed fields.

  4. Create the signed certificate in PEM format

    openssl x509 -req -days 7300 -in secdmgbuild.csr -CA casecdmg.crt -CAkey casecdmg.key -set_serial 01 -out secdmgbuild.crt
  5. Convert the signed certificate to DER format

    openssl x509 -in secdmgbuild.crt -inform pem -out secdmgbuild.der -outform der   
  6. Bundle the PEM certificate and private key into a PKCS#12 package

    openssl pkcs12 -export -in secdmgbuild.crt -inkey secdmgbuild.key -out secdmgbuild.p12
  7. Use hdiutil with the -certificate options to create an encrypted volume (example only):

    hdiutil create -type SPARSE -encryption aes-256 -certificate ~/certsecdmg/secdmgbuild.der -fs HFS+J -volname "SecureImage" -size 100m ~/Desktop/SecureImage
  8. Import secdmgbuild.p12 in your keychain
  9. Double-click SecureImage.sparseimage, enter: password of step 3/always allow to always allow access for diskimages-helper.
  10. Create a new Automator workflow, adding a Run Shell Script action with the following command:

    hdiutil mount ~/Desktop/SecureImage.sparseimage

    (please apply paths as needed)

    This simple Automator workflow works as "workflow" and "app".

  11. Add further actions as required.
  12. Save the content of the folder certsecdmg at a secure place and remove it afterwards.
  • @user3439894 it may require some input which depends on "@user3439894 I can't just double click because there is more to the workflow than just mounting the image. – OrigamiEye 8 hours ago"
    – klanomath
    Commented Dec 24, 2019 at 16:33
  • 1
    @user3439894 Another quote: "Instead of dragging and dropping the dmg file I want to double click the created workflow and have it mount a specific file." The simple workflow consisting of the "run shell script ..." action only, works as workflow as well as app (both tested).
    – klanomath
    Commented Dec 24, 2019 at 16:35
  • This is interesting but not what I was looking for.
    – OrigamiEye
    Commented Dec 25, 2019 at 16:27
  • I wanted to acknowledge your efforts and provide a reason why I won't accept it.
    – OrigamiEye
    Commented Dec 25, 2019 at 16:39

The code in my AppleScript was causing problems.

The full automator flow is 2 Apple Scripts, one to set the variable for the file location and another to run it.

The first script:

on run {input, parameters}

    set output to "NameOfImage"

    return output
end run

The next one

on run {input, parameters}
    set imagePath to "Macintosh HD:Rest of Path:" & (item 1 of input) & ".dmg"
    tell application "DiskImageMounter"
            open alias imagePath
        end try
    end tell
end run

Running the previous code in Script Editor produced an error message instead of timing out.

error "DiskImageMounter got an error: Connection is invalid." number -609

I don't know why a try statement fixed it or why it needs the alias, but there is not much information available on AppleScript.


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