Included in my thesis is to create an administration interface, in which an administrator can approve users whom have asked for access to use OpenNebula.

Upon approval the users should be added to OpenNebula (i.e. it corresponds to the command oneadmin createuser username password). (More information of the interface (section 4.2).)

I am trying to perform this with an execution of a shell command in a PHP file. Why doesn't this work (below is just a specific example - not the general code that I am using)?

$execQuery = "/bin/su oneadmin postgres -c '/usr/bin/oneuser create test10 test10'";
shell_exec ($execQuery); //execute query in shell.

Nor does this work (even though I am logged in as oneadmin, when the script is executed by PHP):

shell_exec ("/usr/bin/oneuser create test10 test10");

It works when I type that command in the shell. I have tried to execute other shell commands through php and those work fine, so I wonder where the problem lies.

I have given the file /usr/bin/oneuser rwx rights for all users.

  • 1
    What happens when you run your code? Are there any visible effects (output, log messages, …)? What happens if you put id or sleep 10 as the command? Commented Jun 19, 2011 at 11:20
  • Thanks for the reply! I get no output. Shell_exec ("sleep 10") and many other shell-commands works. Commented Jun 19, 2011 at 12:32
  • shell_exec returns the output as a string. Does the oneuser command produce any output? Try printing out the return value instead of discarding it. Does the command produce any error output? If you run shell_exec("echo 1>&2 this is an error"), where does the error message end up? Commented Jun 19, 2011 at 12:40
  • Is it just me or is the commands shows here really confusing. Su is running a program called oneadmin and being told to run postgres with a command that starts with a full string to another program that creates a user? No wonder to poor guy can't figure out which part of the chain is broken. Or does it not go together like that?
    – Caleb
    Commented Jun 19, 2011 at 19:01

4 Answers 4


On the php manual for shell_exec, it shows that the function returns the output as a string. If you expect output from the program you launch, you need to capture this like so:

$execQuery = "echo -n test_command";
$output = shell_exec($execQuery);
echo $output;

Your question doesn't show trying to capture any data. If you also make sure to connect stdout and stderr when you run your command, you should get a better idea is what is going on. To use your example:

$output = shell_exec("/usr/bin/oneuser create test10 test10 2>&1");

That should help you see what is going on. As Shadur suggests, it seems likely that these programs expect an interactive terminal that can enter passwords in order to run. Even if don't need input, they might expect interactive shells. And he's right that su doesn't play nice in this context. There is, however, a correct tool for the job.

You can setup sudo to such that your http user can execute your program as username without a password but NOT be able to do anything else by running visudo or whatever you use to edit your sudoers file and adding this line:

http    ALL=(username) /usr/bin/oneadmin

Then in php your command would look something like this:

$execQuery = "sudo -u username /usr/bin/oneadmin postgres -c '/usr/bin/oneuser create test10 test10'";
$out = shell_exec ("$execQuery 2>&1");
echo $out
  • Thanks for your help! I know get this error: "testsudo: no tty present and no askpass program specified" Commented Jun 21, 2011 at 10:35

Try passthru($cmd);

It will allow user's I/O on the Terminal screen.


In the first case, su generally asks for a password when you run it; shell_exec doesn't handle interactivity well.

I don't know oneuser, maybe it's trying to ask for some password as well?


First you need to permit your Webserver to Execute System commands. However in my instants I will be using CentOS6.3 64bit LAMP server.

First of all we need to know our current user that our apache uses, in most case its apache, lets check the the user name by PHP to make sure our username.

    echo shell_exec("whoami");

in my case the output was apache, now let us edit the sudoer and give permission for our apache.

type below command to enter the sudoer file.


now append the below line end of your file, by this your apache will get full root access from PHP script.


Now run below script from your PHP, this your should see the user as root,

    echo shell_exec("sudo whoami");

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