ImageMagic Permission denied on IIS - pdf

Question

I have ImageMagick-6.9.2-8-Q16-x64-dll.exe installed with GhostScript on Windows Server 2012 R2.
Executing convert "document.pdf" "thumbnail.jpg" command line from PHP using shell_exec or exec fails by returning a value of 1. If I ran the same command manually in Command Prompt(cmd.exe) it creates the pdf file seamlessly.

Answer 1

After going through many articles and forums, these are the steps I followed to make ImageMagic work on IIS environment.
Temp directory permission:
Whenever PHP uploads a file to the server, IIS will place the file to C:\Windows\Temp directory and move it to the destination directory. In this process the uploaded file will inherent ownership and permission from the Temp directory. By default this inheritance will prevent ImageMagic from accessing it. To overcome this limitation the IUSR and IIS_USRS need to have read/write permission on the Temp directory.
For detail explanation read this article.
Image Magic permission/Application Pool Identity: Since PHP is not allowed to execute convert.exe while being served under the IIS user, you have to create/use default application pool in IIS. Once this pool is configured, you have to grant permission to this pool on the ImageMagic directory and the directory where in the pdf file is placed. For detail explanation read this thread. Note: some articles suggest IUSR or IIS_IUSR should be given permission to execute cmd.exe. This is highly discouraged as it could create a window for the security breach.
Source and destination directory permission: Both of this directories need to have IUSR and IIS_IUSR read/write permissions
Command line syntax: common mistakes while passing arguments to the command line from PHP are paths, back slash need to escaped. For instance instead of passing C:\Inetpub\vhosts\... it should be passed as C:\\Inetpub\\vhosts\\....
Here is an example of a working snippet:
$cmd = 'convert "C:\\Inetpub\\vhosts\\a\\doc.pdf[0]" "C:\\Inetpub\\vhosts\\b\\thumb\\a.jpg"';
$output = "";
$result = exec($cmd, $output);
print_r($output); //var_dump($output);
Notice that the whole command is wrapped with single quote and source and destination files are wrapped with double quotes.
Debugging:
PHP doesn't report any error that might occur during executing command line. If error is encountered it fails silently. To debug output sent from the command line, its recommended to use exec. This function let you pass an output variable that will be populated with an array containing response from the command line. From here you can use var_dump, print_r to display the output. If this value has a value of 1 or 4, it implies you still have permission issue you have to resolve :(
Hopefully this helps.

Answer 2

We observed the same issue in ASP.NET application. We resolved it by making sure that we have disposed the ImageMagick object properly
Note: We wrapped the ImageMagick object inside Using Statement. It didn't work.
We have explicity closed that object.