Asked  8 Months ago    Answers:  5   Viewed   87 times

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, 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.




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.

Wednesday, March 31, 2021
answered 8 Months ago

I already said that I was new to exec() function. After doing some more digging, I came upon 2>&1 which needs to be added at the end of command in exec().

Thanks @mattosmat for pointing it out in the comments too. I did not try this at once because you said it is a Linux command, I am on Windows.

So, what I have discovered, the command is actually executing in the back-end. That is why I could not see it actually running, which I was expecting to happen.

For all of you, who had similar problem, my advise is to use that command. It will point out all the errors and also tell you info/details about execution.

exec('some_command 2>&1', $output);
print_r($output);  // to see the response to your command

Thanks for all the help guys, I appreciate it ;)

Monday, July 12, 2021
answered 4 Months ago

You can run command and display command output into text as below :

public class MainActivity extends Activity {

    TextView tv;

    protected void onCreate(Bundle savedInstanceState) {
        tv.setText("Output :"+"n"+runAsRoot());

    public String runAsRoot() {

        try {
            // Executes the command.
            Process process = Runtime.getRuntime().exec("ls -l");

            // Reads stdout.
            // NOTE: You can write to stdin of the command using
            //       process.getOutputStream().
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(process.getInputStream()));

            int read;
            char[] buffer = new char[4096];
            StringBuffer output = new StringBuffer();
            while ((read = > 0) {
                output.append(buffer, 0, read);

            // Waits for the command to finish.

            return output.toString();
        } catch (IOException e) {
            throw new RuntimeException(e);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);

Note : The "su" command does only run if the device is rooted. Otherwise it throws an exception.

Thursday, July 29, 2021
answered 3 Months ago

It sounds like the program is outputting its warnings to standard error rather than standard output. exec will only catch standard output. I don't know for certain that standard error is always sent to the apache error log, but it seems likely.

If you don't need compatibility with non-*nix systems, you can redirect standard error to standard output by appending 2>&1 to the command:

exec('some_command --option 2>&1', $output, $ret);

This should both make the warnings available to your php program and prevent unnecessary logging.

Wednesday, August 4, 2021
answered 3 Months ago

Depends on the OS you are using.

For linux:

pclose(popen("php somefile.php &","r"));

notice the amperstand at the end (very important).

For windows:

pclose(popen("start php.exe somefile.php","r"));

here the start keyword is important.

Hope this helps.

Tuesday, October 12, 2021
answered 2 Weeks ago
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