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I have a certain PHP script that calls exec() to execute a command to convert a PDF to JPG. This command works fine in bash.

To preempt your initial troubleshooting guesses, note the following:

  • safe_mode = Off
  • Permission on the directory containing the PDF and the script is set to 777, and this directory is also where the JPG is being written.
  • The command I am passing to exec() explicitly points to the binary being used (e.g. /usr/local/bin/convert).
  • display_errors = On
  • error_reporting = E_ALL
  • disable_functions = [blank]
  • I am echoing exec()'s output and it returns nothing. The command being run by default returns nothing.

When I call this PHP script from the browser (visiting http://www.example.com/script.php), exec() does not execute its argument.

IMPORTANT: I know that there are no issues with my script or the way I have constructed the bash command, because from bash, I can execute the script with 'php' and it works (e.g. 'php script.php' converts the file)

I have also tried switching out exec() with system().

Last, I have had this issue once before in the past but cannot remember how I fixed it.

I know there is something I am missing, so I hope someone else has experienced this as I have and remembers how to fix it!

Thank you in advance for any assistance you can provide.

Alex

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What are the arguments being passed to convert? Do they include the full path to the file? – Powerlord Feb 11 '09 at 21:47
In PHP 5 make sure to use E_ALL | E_STRICT for complete error reporting. – Ross Feb 12 '09 at 18:33
UPDATE -- IMPORTANT: I found that this was an issue with ImageMagick, and accomplished the PDF to JPEG conversion with GhostScript (with a much longer command) instead of using ImageMagick as a middle-man. There were no issues with PHP, my permissions, or exec(). Thank you For all of your input! – user60264 Feb 12 '09 at 21:26
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8 Answers

up vote 18 down vote

Add 2>&1 to the end of your command to redirect errors from stderr to stdout. This should make it clear what's going wrong.

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Yep, I'm getting a strange ImageMagick error: convert: missing an image filename `test.jpg' @ convert.c/ConvertImageCommand/2766. After searching around a bit with Google, it looks like it could be a buggy release. I'm rebuilding the latest stable revision and testing in a few minutes. – user60264 Feb 12 '09 at 17:57
that is an excellent tip! – bzx Jun 19 at 12:26
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up vote 4 down vote

Just some guess, it might be that your webserver process user does not have privileges to do so.

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Excellent! This is a very good point. If calling a bash script with exec (through php) then make sure the bash script is readable by Apache too. – mr-euro Nov 16 '10 at 16:34
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up vote 3 down vote

Since it works when from the command-line (which would be under your own user account), it sounds to me like the account the web server is running under (often "www-data") does not have execute permissions on the conversion program.

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How can someone give permissions? – salamis Dec 23 '11 at 22:22
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up vote 2 down vote

Does your Apache/webserver user have the necessary rights to run the shell command?

When you run from the cl you are likely running as a different user, which may explain which cl works but via browser doesn't.

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up vote 1 down vote

Have you considered file permissions? In the browser, php is running under one user, but when you run it in bash, it is likely running with your user permissions.

It's the first thing I would check.

Amy

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up vote 1 down vote

It may be due to the different users running the script through the web server and the script through bash.

Normally the scripts/exec invoked through server as with user 'www' and this user dont have any write access to your area. but when you run the script in bash then you do have write permissions.

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up vote 0 down vote

I have determined that this is an issue with ImageMagick, not PHP. I am attempting a few fixes, and if they don't work, I'm going to end up using some PHP shared library (probably imagick) to do the work instead.

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up vote 0 down vote

Default output device is changed.

login as www (after enabling) gives output through shell, but not through php.

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