php - How to exec in background multiple bash command

Question

I'm trying to run in background two bash command using exec function.

 $action[] = "/path/script1 par1 > log1 2>&1";
 ...
 $action[] = "/path/script2 par2 > log2 2>&1";
 ...
 $cmd = "( " .implode(' && ',$action). " ) &";
 exec($cmd);

script1 and script2 are bash scripts.

Scripts are properly executed and their output is correctly saved in their log files, but my application hangs. It seems that last & doesn't work.

I have already tried:

 $cmd = "bash -c \"" .implode(' && ',$action). "\" &";

If I run a single command, it works in background.

I captured $cmd and if I run:

 ( /path/script1 par1 > log1 2>&1 && /path/script2 par2 > log2 2>&1 ) &

from command line, it works in background.

I'm using Apache/2.0.52 and PHP/5.2.0 on Red Hat Enterprise Linux AS release 3 (Taroon Update 2)

Michael Jaros · Accepted Answer · 2015-03-10 19:40:58Z

1

The answer is hidden in the PHP exec documentation:

If a program is started with this function, in order for it to continue running in the background, the output of the program must be redirected to a file or another output stream. Failing to do so will cause PHP to hang until the execution of the program ends.

Add a redirection to the top level of your command line:

exec( "bash -c \"( ./script1 par1 > log1 2>&1 && ./script2 par2 > log2 2>&1 ) \" >/dev/null 2>&1 & " );

and without bash -c:

exec( "( ./script1 par1 > log1 2>&1 && ./script2 par2 > log2 2>&1 ) >/dev/null 2>&1 & " );

Tested with PHP 5.3.3-7 (command line invocation): Program hangs before adding the redirect operators, and terminates afterwards.

answered Mar 10, 2015 at 19:40

Michael Jaros

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