PHP exec() does not run all commands

Question

I am using PHP-FPM with Nginx on Ubuntu. I am trying to launch a PHP task from a web application.

The following two examples work correctly when I run the files from CLI, but not from Nginx.

exec("notify-send 'Starting master at ".date("h:m:s")."'");
echo exec("/home/rohit/Projects/webapp/console/index.php blast 23");

These two work correctly from both CLI and Nginx.

echo exec("whoami");
echo exec("pwd");

I tried changing the PHP-FPM user from www-data to rohit (my username), but no luck. What am I doing wrong?

Did you check the php-fpm error log? Or just set E_ALL and display_errors=on — tylerl
– tylerl, Commented Oct 3, 2012 at 9:12
This is on a development machine, so all errors are on. I checked through shell (su www-data), and all the commands except notify-send worked correctly. notify-send failed silently. My mistake using notify-send for debugging. — Rohit
– Rohit, Commented Oct 3, 2012 at 9:27

tylerl · Accepted Answer · 2012-10-03 15:42:15Z

1

The problem is that you're running notify-send from a service. Notify-send is a desktop-oriented program which interacts with the display. But nginx runs without being attached to a display.

Imagine, for example, that there are 3 people logged on to the computer at the same time, all with different displays. When notify-send runs, it wouldn't know which display to send the notification to.

answered Oct 3, 2012 at 15:42

tylerl

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2 Comments

Rohit Over a year ago

Makes sense - without a X display available to hook into, notify-send (as launched by www-data) must have been shooting messages into a blackhole. Something to keep in mind when launching tasks through exec().

tylerl Over a year ago

Presumably if you set $DISPLAY you could make it work. But still there's some x auth stuff that has to fit, so don't depend on it.

Andreas Linden · Accepted Answer · 2012-10-03 09:07:12Z

1

propbaly the user running the nginx server has no access to /home/rohit and the notify-send command...

eighter give the nginx user the rights to execute those command and script or move them to a location he has access to.

answered Oct 3, 2012 at 9:07

Andreas Linden

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2 Comments

Rohit Over a year ago

Indeed. The notify-send command is not available to www-data (checked from CLI). The console script itself can be run by www-data.

Rohit Over a year ago

@tylerl explains the situation better - why notify-send itself was appearing "to fail".

Taizo Ito · Accepted Answer · 2012-10-04 01:32:26Z

0

See what the standard error message looks like. You can see it by specifying the second parameter in the exec() function.

exec("notify-send 'Starting master at ".date("h:m:s")."' 2>&1", $output);
print_r($output);

The following code may work. In addition, /etc/sudoers also needs to be modified.

<?php
exec("export DISPLAY=:0 && export XAUTHORITY=/tmp/.gdmXXXXXXX && sudo /usr/bin/notify-send test 2>&1", $output);
print_r($output);
?>

The value of XAUTHORITY variable depends on your environment.

Also, /etc/sudoers needs to be changed as follow:

#Defaults    requiretty
 :
www-data ALL=(ALL) ALL
www-data ALL=(ALL) NOPASSWD: /usr/bin/notify-send

Please pay attention to security issues when you do that.

answered Oct 4, 2012 at 1:32

Taizo Ito

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1 Comment

Rohit Over a year ago

This will be useful for interacting with the desktop, but diverging from my intention - verify exec() was launching my scripts. notify-send "not working" was a red herring.

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