laravel4 composer install 得到 proc_open not available 错误

Now I am trying to use composer to install my php package but I got this error message: $ composer install

Loading composer repositories with package information
Installing dependencies (including require-dev)
  - Installing filp/whoops (1.0.7)
    Downloading: 100%          

[SymfonyComponentProcessExceptionRuntimeException]                                   
The Process class relies on proc_open, which is not available on your PHP installation. 

edit :

after enable the proc_open function I got this error and also set my php memory_limit to 384M :

Fatal error: Uncaught exception 'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php:990
Stack trace:
#0 [internal function]: ComposerUtilErrorHandler::handle(2, 'proc_open(): fo...', 'phar:///usr/loc...', 990, Array)
#1 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(990): proc_open('stty -a | grep ...', Array, NULL, NULL, NULL, Array)
#2 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(832): SymfonyComponentConsoleApplication->getSttyColumns()
#3 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(797): SymfonyComponentConsoleApplication->getTerminalDimensions()
#4 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(731): SymfonyComponentConsoleApplication->getTerminalWidth()
#5 phar:///usr/local/bin/com in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php on line 990

解决方案

You should use php-cli to by-pass disable_functions temporarily.

php -d "disable_functions=" /path/to/composer install