Question

I’m trying to back a database via a PHP script using this one simple line:

passthru("/usr/bin/mysqldump --opt --host=localhost --user=\"myuser\" --password=\"mypass\" db_name > /var/www/vhosts/mydomain.com/httpdocs/tools/dbbackup-2011-12-17.sql");

I get no errors or warnings or anything. but if I copy that string and execute it exactly as is on the server via SSH it works perfectly.

/usr/bin/mysqldump --opt --host=localhost --user="myuser" --password="mypass" db_name > /var/www/vhosts/mydomain.com/httpdocs/tools/dbbackup-2011-12-17.sql

I tried using exec() and system() instead of passthru() but same results. This is really strange and I can’t focure out what could be the problem. Any ideas?

Answer 1

An educated guess

If I can make an educated guess it’s because the user that runs the php-script (ie. user the httpd is run as) doesn’t have permission to write to /var/www/vhosts/mydomain.com/httpdocs/tools/.

Though the user you are using to execute the command has.

---

STDERR and STDOUT

To see if there is anything printed to STDERR that is relevant to the problem, use the below snippet!

$tubes = array(
  0 => array("pipe", "r"),
  // print contents on STDOUT to file
  1 => array("file", "/var/www/vhosts/mydomain.com/httpdocs/tools/dbbackup-2011-12-17.sql", "w"),
  2 => array("pipe", "w")
);

$p_handle = proc_open (
  "/usr/bin/mysqldump --opt --host=localhost --user=\"myuser\" --password=\"mypass\" db_name",
  $tubes, $pipes
);

if (is_resource ($p_handle)) {
    fclose ($pipes[0]);

    $stderr_data = stream_get_contents ($pipes[2]); fclose($pipes[2]);

    $proc_ret    = proc_close ($p_handle);

    echo "--------- STDERR:\n$stderr_data\n";
    echo "------------ RET: $proc_ret\n";
} else {
  die ("Unable to execute external resource, aborting!");
}

---

Check the log files!

Have you checked the error_log associated with your httpd?