如何让iOS运行子流程？

I am writing an app for iOS that will start the php binary as a sub process.

The following code is used:

NSString * command = @"/bin/sh -c '";
command = [command stringByAppendingString:[BibleditPaths php]];
command = [command stringByAppendingString:@" -v' > /tmp/php.txt 2>&1"];
int output = system ([command UTF8String]);
NSString* msg = [@(output) stringValue];
NSLog(msg, @"");

The php binary can be started on a jailbroken iPad from the command line. This is the output:

PHP 5.4.31 (cli) (built: Aug 19 2014 11:06:21) 
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2014 Zend Technologies

When starting the php binary from the code above, iOS sends the SIGKILL signal. The php binary does not run or produce any output.

/bin/sh produces this output:

sh: line 1:  2806 Killed: 9               /bin/sh -c '/var/mobile/Applications/DFE552CC-ECBE-4A73-82CF-24870E5D9F62/Library/usr/local/bin/php -v' > /tmp/php.txt 2>&1
2014-09-15 17:33:41.676 PHPRunner[2804:60b] 35072

What can I do to get iOS to run this process successfully?