title: Composer - PHP Warning: proc_open(): fork failed - Cannot allocate memory
body: <p>I have a problem with <strong>composer</strong>, it has always worked well but now it doesn't want to...<br>
  Here is the result of a simple <code>composer install</code> command :</p>
  
  <pre><code>bob@SRV04:~/testdir$ composer install
  Loading composer repositories with package information
  Updating dependencies
  Package operations: 44 installs, 0 updates, 0 removals
    - Installing psr/container (1.0.0): The following exception is caused by a 
  lack of memory or swap, or not having swap configured
  Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open- 
  fork-failed-errors for details
  
  PHP Warning:  proc_open(): fork failed - Cannot allocate memory in 
  phar:///bin/composer/vendor/symfony/console/Application.php on line 952
  
  Warning: proc_open(): fork failed - Cannot allocate memory in 
  phar:///bin/composer/vendor/symfony/console/Application.php on line 952
  
  [ErrorException]
  proc_open(): fork failed - Cannot allocate memory
  </code></pre>
  
  <p>The problem is, <strong>given the state of my memory, everything should work</strong>.</p>
  
  <pre><code>free -h
               total       used       free     shared    buffers     cached
  Mem:          7,8G       3,4G       4,4G       131M       207M       503M
  -/+ buffers/cache:       2,7G       5,1G
  Swap:         1,7G       728M       971M
  </code></pre>
  
  <ul>
  <li>I updated everything I could update</li>
  <li>php.ini memory is set to -1</li>
  </ul>
  
  <p>I saw that there are several other questions that resemble this problem but none of them propose a solution that fixes the bug</p>