cd ~/
mkdir php
cd php
apt-get source php5
cd php5-*/ext/pcntl
phpize
./configure
make
no=`phpize | grep "Zend Module Api No" | cut -d : -f2 | awk '{gsub(/^ +| +$/,"")}1'`
cp modules/pcntl.so /usr/lib/php5/$no/
echo "extension=pcntl.so" > /etc/php5/conf.d/pcntl.ini