Unable to run a command from php to linux - php

Question

I was trying to run a command from PHP to my Linux server but I'm having some trouble with one command:
This is the script:
<?php
$output=null;
$retval=null;
exec('speedtest -L -f, --format=json 2>&1', $output, $retval);
echo "Returned with status $retval and output:\n";
print_r($output);
?>
The output is:
Returned with status 134 and output:
Array ( [0] => terminate called after throwing an instance of 'std::logic_error'
[1] => what(): basic_string::_M_construct null not valid
[2] => Aborted (core dumped))
The user that runs the script is: www-data
if I try to run it directly on the terminal it works.
command from terminal: sudo -u www-data speedtest -L
output: {"type":"serverList","timestamp":"2021-02-23T09:20:51Z","servers":[{"id":4302,"name":"Vodafone IT","location":"Milan","country":"Italy","host":"speedtest.vodafone.it","port":8080},{"id":7839,"name":"Fastweb SpA","location":"Milan","country":"Italy","host":"spd-pub-mi-01-01.fastwebnet.it","port":8080},{"id":11427,"name":"EOLO","location":"Milan","country":"Italy","host":"test.eolo.it","port":8080},{"id":1434,"name":"CWNET","location":"Milan","country":"Italy","host":"speedtest.cheapnet.it","port":8080},{"id":3667,"name":"TIM SpA","location":"Milan","country":"Italy","host":"speedtestmi1.telecomitalia.it","port":8080},{"id":8211,"name":"CDLAN S.R.L.","location":"Milan","country":"Italy","host":"speedtest.cdlan.it","port":8080},{"id":11675,"name":"Italiaonline Supernap","location":"Milan","country":"Italy","host":"speedtest-supernap.italiaonline.it","port":8080},{"id":20551,"name":"Optima Italia","location":"Milan","country":"Italy","host":"mi-speedtest.optimaitalia.com","port":8080},{"id":26415,"name":"P-Lab","location":"Milan","country":"Italy","host":"speed.speedymilan.net","port":8080},{"id":19177,"name":"Seeweb","location":"Milan","country":"Italy","host":"ookla-mil.seeweb.it","port":8080}]}
If I run another command it works perfectly:
<?php
$output=null;
$retval=null;
exec('whoami', $output, $retval);
sleep(1);
echo "Returned with status $retval and output:\n";
print_r($output);
?>
The output is:
Returned with status 0 and output: Array ( [0] => www-data )
Do you guys have any suggestions?

Answer 1

I figured out a way to make it work but probably isn't the best one:
<?php
// attributes
private $output;
private $retval;
private $command;
// methods
function get_serverUpdates($user, $password) {
$command = 'echo '.$password.' | su -l '.$user.'-s /bin/bash -c "speedtest -L -f, --format=json" 2>&1';
$resl = exec($command, $output, $retval);
return json_decode(substr($resl, 10));
}
?>
It does return the correct information.
I think the problem was that as #MarkusZeller said that www-data doesn't have the permission to run all the programs installed.