If you are not the root on the machine, and exec() function is disabled, then you can't enable it by yourself.

See http://php.net/manual/en/ini.core.php#ini.disable-functions

disable_functions string

This directive allows you to disable certain functions for security reasons. It takes on a comma-delimited list of function names. disable_functions is not affected by Safe Mode.

Only internal functions can be disabled using this directive. User-defined functions are unaffected.

This directive must be set in php.ini For example, you cannot set this in httpd.conf.

The Apache’s user www-data need to be granted privileges to execute certain applications using sudo.

1. Run the command sudo visudo. Actually we want to edit the file in etc/sudoers.To do that, by using sudo visudo in terminal ,it duplicate(temp) sudoers file to edit.
2. At the end of the file, add the following ex:-if we want to use command for restart smokeping and php command for another action in your question,

www-data ALL=NOPASSWD: /etc/init.d/smokeping/restart, usr/bin/php

(This is assuming that you wish to run restart and php commands using super user (root) privileges.And you use php command in usr/bin/ path )

However, if you wish to run every application using super user privileges, then add the following instead of what’s above.You might not want to do that, not for ALL commands, very dangerous.

www-data ALL=NOPASSWD: ALL

3.After edit the sudoers file(by visudo we edit the temp file of sudoers so save and quit temp file(visudo) to write in sudoers file.(wq!)

4.That’s it, now use exec() or shell_exec in the following manner inside your xxx.phpscript.keep remember to use sudo before the command use in the php script.

ex:-

exec ("sudo /etc/init.d/smokeping restart 2>&1");

or

shell_exec("sudo php -v"); 

So in your problem,add the commands that you wish to use in to the step no (2.) as I add and change your php script as what you want.

here is the same problem as yours https://stackoverflow.com/a/22953339/1862107

Apach may be configured to disallow calling some command/libs...

But maybe environment variables (e.g. $PATH...) are not just the same for your user and Apach user (www-data) or something like that.

Here is an example what you can do to search the issue:

Try to call set or setenv to get the list of the variables.

Create a basic script callset.sh:

#!/bin/bash
set

(do not forget chmod +x callset.sh to give execution permission):

Then call this bash script from PHP:

$output = shell_exec ('/your/dir/callset.sh 2>&1');
echo $output

or

exec ("/your/dir/callset.sh", $output, $exitstatus);
print_r ($output);

Then check the difference with your own set call.

Finally provide the missing variables like that:

$output = shell_exec('PATH=aaa:bbb:ddd unoconv -f pdf test.odp 2>&1');

1) Check the security setup

Can shell_exec() be run or not? If it can't then it's because you are having some security settings enabled.

The problem is that shell_exec() and exec() can be disabled for security reasons. This can be changed by editing PHP's disable_functions option.

INI settings are usually stored in specific *.ini files under the /etc/php/* directories. So you have to look for some settings in there. You’ll find several INI settings, depending on how PHP is run. To find them :

find /etc/php/ -iname 'php.ini'

This could output something like this :

/etc/php/8.2/fpm/php.ini
/etc/php/8.2/apache2/php.ini
/etc/php/8.2/cli/php.ini
/etc/php/8.2/cgi/php.ini

To see the settings and which INI file is loaded, add this at the beginning of your script and call it via your web server :

phpinfo();
die();

You'll see all the loaded INI files and what is set on the disable_functions option.

/etc/php/8.2/cli/php.ini is probably setting disable_functions to an empty string, meaning that in command line there's no restriction. But for the other INI files, this option might contain a list of functions that you won't be able to run. Edit this option if needed. But be always aware that giving your server the ability to run some binaries can lead to some security issues if your app is taking some user input to build the command.

Apache configuration can also set some PHP settings, just for a specific Virtual Host. So have a look at them if you can't find something in the php.ini files.

Depending on your PHP setup, you may also have to check safe_mode and suhosin.executor.* if you have the Suhosin hardening module installed.

2) Verify that you can run shell_exec

There are several ways to run a binary. shell_exec is equivalent to the built-in backtick operator. So if shell_exec is listed in the disable_functions option then you won't be able to use the backtick operator.

If you get an error 500 then it's typically because you cannot run shell_exec. If you check /var/log/nginx/error.log or /var/log/apache2/error.log with this command :

sudo tail -f /var/log/{apache2,nginx}/error.log

It will print both logs until you press CTRL+C. You may see this error :

PHP Fatal error:  Uncaught Error: Call to undefined function shell_exec()

PHP also offers exec(), passthru(), system(), and the proc_*() functions. So you've got several possibilities to try and run your command.

Have a try with a simple PHP code :

<?php

header('Content-Type: text/plain; charset=utf-8');

echo 'PHP user given with the "id" command: ' . `id`; // equivalent to shell_exec('id');
echo 'System date is ' . `date --iso-8601=seconds`;

This should output RAW text in your browser with :

PHP user given with the "id" command: uid=33(www-data) gid=33(www-data) groups=33(www-data)
System date is 2023-09-29T11:50:28+00:00

3) Use a full path to the binary

When shell_exec() is run from the web server, it's rather common that the binary isn't found in the PATH. Usually, the www-data user running PHP won't even have a shell. But this user can normally run some binaries, except if some settings at point 1 is blocking it.

To find the full path to a binary, use the which command :

which wkhtmltopdf

This should output the full path to the binary. Certainly something such as /usr/bin/wkhtmltopdf.

Now replace your PHP code with the full path to the binary:

header('Content-Type: text/plain; charset=utf-8');
echo shell_exec('/usr/bin/wkhtmltopdf --version');

Does it print wkhtmltopdf 0.12.6 like expected?

If no, then we have to investigate more at the next point.

4) Get the execution output and find errors

This can be done with the help of exec(), passthru() or system() as they all return the execution status code.

With the proposition of Volkerschulz, we'll also redirect the standard error stream to the standard output stream so that we can see some details that may have only be printed to the error stream.

This is done by redirecting stderr (2) into stdout (1) by adding 2>&1 after your command.
Just as info, stdin is 0.

In PHP, this becomes :

<?php

header('Content-Type: text/plain; charset=utf-8');

$command = '/usr/bin/wkhtmltopdf --wrong-option 2>&1';

$last_line = exec(
  $command,    // The command to execute.
  $output,     // A variable that will be filled with an array of all the lines returned.
  $result_code // The return status of the executed command.
);

var_export([
  '$command' => $command,
  '$output' => $output,
  '$last_line' => $last_line,
  '$result_code' => $result_code,
]);

This outputs :

array (
  '$command' => '/usr/bin/wkhtmltopdf --wrong-option 2>&1',
  '$output' => 
  array (
    0 => 'Unknown long argument --wrong-option',
    1 => '',
    2 => 'Name:',
    3 => '  wkhtmltopdf 0.12.6',
    ...
    ...
    95 => '',
  ),
  '$last_line' => '',
  '$result_code' => 1,
)

Now I'm able to see that I got a $result_code of 1 instead of 0.

In case the executable is having other errors, you'll see them in the $output array as the stderr stream should be visible. This should help you find how to fix the issue. Probably some other security problems due to the fact the www-data user might be missing some rights, paths or whatever.

PS: On my Vagrant box of Ubuntu 22.04, I managed to run wkhtmltopdf without errors on both Apache and NGINX.

Don't forget also that your www-data user should have write access to the destination folder where you are producing the PDF file.

5) Try re-installing wkhtmltopdf and/or use a PHP wrapper

You might have to re-install wkhtmltopdf if it's not properly working :

sudo apt remove wkhtmltopdf
sudo apt autoremove
sudo apt install wkhtmltopdf

You can also try using a PHP wrapper library for wkhtmltopdf called Snappy. It might be useful.

6) Switch to an alternative in pure PHP if necessary

Perhaps you won't manage to make wkhtmltopdf work that easily. It's a pity as it's effectively a fast and reliable solution.

But to create a PDF from HTML you could also use the Dompdf PHP library. I've used it in the past and was happy with it.

I've tested your code and in my server it works correctly. It gives the following output:

Output: apps awstats cgi-bin clients conf error html icons ispconfig manual mauco.org med-01.uc.cl php-fcgi-scripts usage

That are the folders in /var/www

I think you may have a privileges issue. What happens if you try with this command:

  $output = shell_exec("ls /tmp");

You can also check if what user is being used by apache/nginx

 $output = shell_exec("whoami");

Please include screenshots of your results.

If you say it works on the terminal and not on apache then apache's php.ini file may be disabling the use of shell_exec().

See http://www.php.net/manual/en/ini.core.php#ini.disable-functions

Your apache's php.ini file may look something like

disable_functions=exec,passthru,shell_exec,system,proc_open,popen

Remove shell_exec from this list and restart the web server, although this is a security risk and I don't recommend it.

You probably need to chdir to the correct directory before calling the script. This way you can ensure what directory your script is "in" before calling the shell command.

$old_path = getcwd();
chdir('/my/path/');
$output = shell_exec('./script.sh var1 var2');
chdir($old_path);
echo "<pre>$output</pre>";

The question is a bit old, but for those who experience this problem can try to set the environment variables of direct on the server. PHP uses the putenv () function.

Example:// Set Variable Enviromental

$JAVA_HOME = "/usr/lib/jvm/java-8-oracle"; 
$ANDROID_HOME = "/opt/android-sdk-linux";
$PATH="$JAVA_HOME/bin:/usr/local/bin:/usr/bin:/bin:$ANDROID_HOME/platform-tools:$ANDROID_HOME/tools:$ANDROID_HOME/build-tools/24.0.0-preview";

putenv ("JAVA_HOME = $JAVA_HOME"); 
putenv ("PATH = $PATH");