PHP Calling shell_exec on a bash script running a background process times out

Question

I have a bash script with a few lines similar to the following

echo "Do something"
/bin/sh -c 'echo $$>pidfile && exec "command"' &
echo "Ran Command">/path/to/outputfile.txt
exit 0

Then I call that from a PHP script
return shell_exec("/path/to/bash/script arguments");

Now, when I do that, the command is run successfully, and outputfile.txt contains "Ran Command".

However, the PHP script times out after 10ish seconds. The bash script takes about 2-3 seconds to run

If I change the line to return shell_exec("/path/to/bash/script arguments >/dev/null 2>&1");

Then it executes and the PHP script doesn't time out.

I understand why redirecting the output lets PHP continue executing, but I can't figure out why PHP is timing out in the first place requiring me to do that. Can someone give me some assistance with this?

The bin/sh should use 2>&1 & instaed of & only, because you are moving the script into the background, but the outpu is still piped whitin the bash script. maybe PHP waits vor stdin/stderr to close. — JustOnUnderMillions
– JustOnUnderMillions, Commented Sep 2, 2016 at 14:34
If that was the case, shouldn't the same timeout (or apparent hang) occur if I manually run /path/to/bash/script arguments? It doesn't. Only when I run that through php's shell_exec() does the time out happen. — Trel
– Trel, Commented Sep 2, 2016 at 14:35
>/dev/null 2>&1 & look here unix.stackexchange.com/questions/70963/… — JustOnUnderMillions
– JustOnUnderMillions, Commented Sep 2, 2016 at 14:36
the same timeout maybe you will not see an output, but the /bin/sh can still be running. check this with htop or ps -Af — JustOnUnderMillions
– JustOnUnderMillions, Commented Sep 2, 2016 at 14:37
@JustOnUnderMillions I was using the >/dev/null part, I knew you meant that. Is there any reason to put it in the bash script rather than the PHP script? — Trel
– Trel, Commented Sep 2, 2016 at 14:54

JustOnUnderMillions · Accepted Answer · 2016-09-02 15:34:05Z

2

Test this two versions and you get it:

test1.sh /bin/sh -c 'sleep 10' >/dev/null 2>&1 &

test2.sh /bin/sh -c 'sleep 10' &

run both with php on command line like

test1.php <?php shell_exec('test1.sh');

test2.php <?php shell_exec('test2.sh');

and see the difference.

test2.sh is taking 10ish seconds and test1.sh is working like your

return shell_exec("/path/to/bash/script arguments >/dev/null 2>&1");

answered Sep 2, 2016 at 15:34

JustOnUnderMillions

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1 Comment

Trel Over a year ago

It does work and I'll mark this as the solution (I'll put the >/dev/null 2>&1 part in the bash script), but I'm still a bit at a loss. Running those under PHP they do behave differently. However, in bash, ./test1.sh and ./test2.sh execute exactly the same,

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