exec() Command Revisited

zonewatcher

I have searched this forum and found several posts relating to Linux, php, and the use of the exec() and shell_exec() commands. However, I have not found a solution that will work.

As stated, I am using Linux (most recent stable ver ... cant remember ver), php 5, apache server. I am trying to execute a php script that will NOT stop the main php program from executing. That is, i want to call the proper function (exec() or shell_exec() ... not sure which) and the program throws that to the command line and moves on to the next, not pausing to wait for the return of the executed command.

I am running script.php which contains ...
$_dummy = exec("php /mnt/notif/external.php 4 5 abc 7 xyz");

This waits for execution and I have tried

$_dummy = exec("php /mnt/notif/external.php 4 5 abc 7 xyz &");

This waits as well ... I have tried

$_dummy = exec("php /mnt/notif/external.php 4 5 abc 7 xyz 1>/dev/null 2>/dev/null");

This waits as well. I am at a loss. Oh ... and I have tried the above with a space and an ampersand on the end. The script called runs properly when called from the command line.

To begin with, should I use exec() or shell_exec()? Then what would the command be to NOT wait for the return from the called script? Any help is greatly appreciated!

Bill

dagon

try:

exec("nohup php /mnt/notif/external.php 4 5 abc 7 xyz");

zonewatcher

That seemed to work. Thanks for your help!

Bill

zonewatcher

Ok ... this seemed to work fine from the command line calling the main script and the called script (with exec()) but when I place it in a cron job, it seems to crap out. Could it be the message about nohup redirecting stderr to stdout? Even though the notification was generated from the command line, everything worked fine.

Any insight is greatly appreciated!

Bill

zonewatcher

What is the difference between exec() and shell_exec()?

NogDog

The differences are the arguments they accept and what they return. See [man]shell_exec/man and exec() for specifics. (I know, RTFM type replies suck, but it's either that or me just copy-and-pasting what the manual says here.)

zonewatcher

I read the manual and the only difference IS what they return. In my situation as described above, neither seem to have and advantage or disadvantage and also it seems that they would work identical (in the above scenario). I am just looking for some rhyme or reason that it worked at the command line and not as a cron job.

When I look at 'top' I only have 2 php instances at any time running. It seems to be waiting on the response. I assume the two instances are the script the cron job calls and the exec() script. Being a novice I probably am missing something but it seems that if the main script is not waiting on the exec()'d script to complete before it continues, there should be multiple exec()'d scripts showing in top. That is provided the exec()'d scripts have not completed .... which they shouldn't with seconds of each top update.

Thanks ... Bill

dagon

shouldn't need nohup for a cron job but you may want to specify the path for php. are you running exec in a cronjob? im a little confused now.

zonewatcher

No, I am running exec from a script that is run by the cron. The script kicked off and is running but, at most, there are only two php processes at one time. The main script appears to be waiting for the return of exec. I call it from the main script (the one started by cron) by:

$_dummy = exec("nohup php /mnt/notifs/utils/script_run_by_cron.php '$current_list' '$key' '$secret' '$id' '$temporary_table_name' '$user_limit'");

The variable all contain valid values and transferred fine run from the command line. I am wondering if maybe even at the command line it was waiting on the exec command to complete and I simply didn't notice it.

Sorry for any confusion! I have been working on this for many hours with no resolve. Could it be that I assign the result of the exec() function to a variable? Could that be telling it to wait? The only thing I haven't tried is exec(command_string) on a line by itself without the $_dummy variable assignment.

Thanks,

Bill

dagon

A test:

cron script:

for ($i = 1; $i <= 10; $i++) {
exec("test.php $i");
}

test.php

sleep(60);

then use: ps ax | grep 'php'

to see it there are the 10 scripts

zonewatcher

Didn't even have 2 do that ... the script that I set in motion over 4 hours ago is still running ... one exec at a time. When I ps I get the main cron script and only one of the execs .... ran it several times and there are only two at a time.

dagon

your server or hosted?

zonewatcher

Ran your script and there were always 2 scripts running ... the calling (test1) and the exec()'d (test). After 60 seconds, the test would have the parameter of 2, 60 more then 3 ... not all at once.

The server is an amazon ec2 cloud. I have an xlarge and large server. Any idea with that?

Thx!

dagon

talk to your hosts support, it sounds like an issue at their end

zonewatcher

Ok ... thanks!

zonewatcher

I can control the configuration. Any idea where the problem may be. I can install software .. just as it were my server.

zonewatcher

I can install software/change configuration. Any idea what may be the issue?

zonewatcher

oops ... sorry .. .didnt mean to post twice ... i failed to look at the second page.