Running exec() command with dev>null & doesn't work, but dev>null does

Question

I have this exec command which runs just fine, but doesn't free up the browser (ie. there is a php timeout issue, but the actual command continues to run):

exec("/usr/local/php53/bin/php csv.php $file $user > /dev/null");

When I run ps auxw I see these two running processes:

sh -c /usr/local/php53/bin/php csv.php /tmp/php9Pwu9e 294  >
/usr/local/php53/bin/php csv.php /tmp/php9Pwu9e 294

However, when I run the code below, the browser immediately is free, but the command doesn't continue to run:

exec("/usr/local/php53/bin/php csv.php $file $user > /dev/null &");

When I run ps auxw I see one running process that dies after 16 seconds (and seems to eat up memory quickly and use a lot of CPU%):

/usr/local/php53/bin/php csv.php /tmp/php9Pwu9e 294

Then the process dies without having actually done anything. Not sure what the ampersand is doing that would cause this.

Also why does sh -c appear when no ampersand is present at the end? I feel that this may be indicative of something, but have no idea what.

EDIT:

Because this keeps cropping up as an answer, I have also tried:

exec("/usr/local/php53/bin/php csv.php $file $user > /dev/null 2>&1 &");

Which demonstrates the same issue as mentioned above. The code below, does run, but does NOT free up the browser.

exec("usr/local/php53/bin/php csv.php $file $user > /dev/null 2>&1");

Try to redirect errors to /dev/null too: `your_command > /dev/null 2>&1 &` — Fabian Schmengler, Jan 28 '13 at 07:45
What happen if you directly run `php csv.php file user` in terminal? — Passerby, Jan 28 '13 at 08:04
It runs properly, the only thing that seems to be throwing it off is the ending ampersand. — kylex, Jan 28 '13 at 08:05
@SalmanA the process isn't actually doing anything. it just builds up memory and uses up CPU% then dies, when it has the ampersand. — kylex, Jan 28 '13 at 15:42
@monkeymatrix yes, and proc_open and passthru. All the same issue. — kylex, Jan 28 '13 at 16:31

score 0 · Answer 1 · answered Jan 28 '13 at 07:45

0

try this instead

exec("nohup php csv.php $file $user > /dev/null &");

answered Jan 28 '13 at 07:45

Kuldeep Singh

696
10
25

Nope, that seems to prevent anything from happening. – kylex Jan 28 '13 at 07:47
You also need to include fab's suggestion of sending errors to /dev/null. – Brent Baisley Jan 28 '13 at 16:26

score 0 · Answer 2 · answered Jan 28 '13 at 17:57

Try both redirecting both the output and the errors to /dev/null (or another output file of your choice, provided that it has write permissions set for the user running the web server), as well as making it a background process with the ampersand, as stated on a PHP manual user note:

<?php

exec("php /var/www/foo.php > /dev/null 2>&1 &");

Just tried it and it works as expected: the calling script finishes right away, and the background process keeps running for as long as it takes to complete.

As stated in the comments, I've tried this approach to no avail. — kylex, Jan 28 '13 at 18:02

score 0 · Accepted Answer · answered Jan 29 '13 at 03:00

The issue was much simpler than I had thought. The problem was the $file (which was an uploaded file being stored in the /tmp directory) was not found. I'm not sure why, but I imagine it has something to do with the file being destroyed before the background process can get to it.

The solution was to move_uploaded_file() the file to a permanent location, and run the script with that file. That worked.

Running exec() command with dev>null & doesn't work, but dev>null does

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