Question

I am trying to send a SIGHUP signal to an external process using PHP. Currently, I am doing the following:

$pid = shell_exec('ps -ef | grep mosquitto | grep -v grep | awk \'{print $2}\'');
shell_exec('kill -s HUP $pid');

When I run “php test.php” from the command line, I have verified that the signal is sent to the correct process, as expected.

When I invoke the script by visiting http://foo.com/bar/test.php, the signal isn’t sent, and shell_exec returns nothing.

For testing, I temporarily ran PHP with root permissions but had the same issue, so I assume this is not a permission issue.

Interestingly, shell_exec returns output for the pwd command and the uptime command to the browser, but not the ls command. But when run from the command line, shell_exec returns output from ls normally.

Is there another limitation of these commands that I’m missing?

Also, a few notes:

• Safe Mode is off
• error_reporting = E_ALL
• No functions are disables
• I have tried explicitly pointing to the binaries (Ex. /bin/ps and sh -c ps)

Answer 1

Try

echo shell_exec('(ps -ef | grep mosquitto | grep -v grep | awk \'{print $2}\') 2>&1');

and see if any errors are reported. Also, you could try pgrep, pkill or killall instead of messing about with ps and grep.

Alternatively, try just running ps and parsing its full output in PHP yourself. (preg_match() and/or preg_grep() may be useful for this.)
And you can use posix_kill() instead of running an external kill program.

Edit: As per comments, it seems the actual issue was a missing or incorrectly set PATH environment variable. One way to solve this issue would be to run echo $PATH in shell, copy the output and set PATH to the same value in PHP with putenv(). Another solution is to use which in shell to determine the full paths to ps et al., and use those full paths in shell_exec().