iWantPiD (http://blog.esin.name/2014/03/pid-linux.html)

i_want_pid.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void main( int argc, char *argv[ ] )
{

    if ( argc != 3 ) exit( 1 );

    char *command = argv[ 1 ];
    int iwp = atoi( argv[ 2 ] );

    if ( iwp > 32767 || iwp < 300) exit( 1 );

    if( access( "stop", F_OK) != -1 ) remove( "stop" );

    if (getpid() == iwp) {
        int th = system( "true" );
    }

    pid_t p;

    while ( 1 ) {

        if( access( "stop", F_OK ) != -1 ) exit( EXIT_SUCCESS );

        if(fork() == 0) {
            p = fork();
            if(p == 0) exit( EXIT_FAILURE );

            if (p == iwp - 2) {
                FILE * F = fopen ( "stop","w" );
                if ( F != NULL ) fclose ( F );
                int th = system( command );
                exit( EXIT_SUCCESS );
            }
            exit( EXIT_FAILURE );
        }
        wait( NULL );
    }

    if( access( "stop", F_OK) != -1 ) remove( "stop" );
    exit( 0 );
}