mkdir php
cd php
apt-get source php5
cd php5-你的版本/ext/pcntl
phpize
./configure
make
cp modules/pcntl.so /usr/lib/php5/你的php扩展库路径/
echo "extension=pcntl.so" > /etc/php5/cli/conf.d/pcntl.ini
ln -s /etc/php5/cli/conf.d/pcntl.ini /etc/php5/conf.d/20-pcntl.ini