What permissions are needed to run a system() command within a php script that writes to a folder?

Question

I've got a php script which has the line:

system("ffmpeg -i ......");

The output folder is set to be:

drwxrwxr-x  5 apache apache   4096 Oct 19 07:40 in_upload

If I run the exact text "ffmpeg -i ......" from the prompt as root, it works fine.

But if the script is run, only a zero sized file is created. Any ideas on what could be wrong?

---

Edit 1

I think I've localized the problem to selinux

I tried the solution recommended in http://www.php.net/manual/en/function.system.php#94929 :

<?php
function my_exec($cmd, $input='')
         {$proc=proc_open($cmd, array(0=>array('pipe', 'r'), 1=>array('pipe', 'w'), 2=>a$
          fwrite($pipes[0], $input);fclose($pipes[0]);
          $stdout=stream_get_contents($pipes[1]);fclose($pipes[1]);
          $stderr=stream_get_contents($pipes[2]);fclose($pipes[2]);
          $rtn=proc_close($proc);
          return array('stdout'=>$stdout,
                       'stderr'=>$stderr,
                       'return'=>$rtn
                      );
         }

echo "1 ";
echo shell_exec('ls');
echo "\n2 ";
my_exec('ls');
echo "\n3 ";
my_exec('/bin/ls');

?>

Output was:

1 
2 
3 

---

Edit 2

AFTER disabling selinux, I got the following results:

echo "1 ";
echo shell_exec('ffmpeg');
echo "\n2 ";
echo system('ffmpeg');
echo "\n3 ";
echo exec('ffmpeg');
===> None worked

echo "1 ";
echo shell_exec('/usr/bin/ffmpeg');
echo "\n2 ";
echo system('/usr/bin/ffmpeg');
echo "\n3 ";
echo exec('/usr/bin/ffmpeg');
===> None worked

echo "1 ";
echo shell_exec('ls');
echo "\n2 ";
echo system('ls');
echo "\n3 ";
echo exec('ls');
===> All 3 worked as expected.

---

Edit 3

php script:

echo "1 ";
echo shell_exec('touch test1.txt');
echo "\n2 ";
echo system('touch test2.txt');
echo "\n3 ";
echo exec('touch test3.txt');

error_log:

touch: cannot touch `test1.txt': Permission denied
touch: cannot touch `test2.txt': Permission denied
touch: cannot touch `test3.txt': Permission denied

php script:

echo "1 ";
echo shell_exec('/bin/touch test1.txt');
echo "\n2 ";
echo system('/bin/touch test2.txt');
echo "\n3 ";
echo exec('/bin/touch test3.txt');

error_log:

/bin/touch: cannot touch `test1.txt': Permission denied
/bin/touch: cannot touch `test2.txt': Permission denied
/bin/touch: cannot touch `test3.txt': Permission denied

php script:

echo "1 ";
echo shell_exec('/bin/touch /var/www/html/beta/test1.txt');
echo "\n2 ";
echo system('/bin/touch /var/www/html/beta/test2.txt');
echo "\n3 ";
echo exec('/bin/touch /var/www/html/beta/test3.txt');

error_log:

/bin/touch: cannot touch `/var/www/html/beta/test1.txt': Permission denied
/bin/touch: cannot touch `/var/www/html/beta/test2.txt': Permission denied
/bin/touch: cannot touch `/var/www/html/beta/test3.txt': Permission denied

Answer 1

A few random thoughts:

• How long does your ffpmpeg command takes ? if it takes longer than the value of max_execution_time in php.ini, I believe that the command is canceled.

• try to use only full paths for the ffmpeg binary and the input/output files. Although, if you have a zero size file outputted, it shouldn't be that.

• Does apache have the permission to run the ffmpeg binary ?

• try a basic command in your system call, such as "touch test.txt" just to check if the problem is from ffmpeg or your php script.

Answer 2

It was a permissions issue, I had selinux enabled. By changing the setting in /etc/sysconfig/selinux

From: 
SELINUX=enforcing

To:
SELINUX=disabled

The system() commands started working