title: Ruby on Rails: permission denied when using "rails generate controller welcome"
body: <p>I used Ruby on Rails on Red Hat server. 
  When I trying to generate a controller file, I got this error:</p>
  
  <pre><code>[ec2-user@ip-172-31-22-128 testApp4]$ rails generate controller welcome
  /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:22:in `initialize': Permission denied @ rb_sysopen - /tmp/spring/fea371aaf9d69cfa58bd12f69b3f1bf6.pid (Errno::EACCES)
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:22:in `open'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:22:in `open'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:22:in `initialize'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:14:in `new'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/server.rb:14:in `boot'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/run.rb:43:in `block in boot_server'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/run.rb:41:in `fork'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/run.rb:41:in `boot_server'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/run.rb:24:in `call'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/command.rb:7:in `call'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/rails.rb:23:in `call'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client/command.rb:7:in `call'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/client.rb:26:in `run'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/bin/spring:48:in `&lt;top (required)&gt;'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/binstub.rb:11:in `load'
  from /home/ec2-user/.rvm/gems/ruby-2.1.2/gems/spring-1.1.3/lib/spring/binstub.rb:11:in `&lt;top (required)&gt;'
  from /home/ec2-user/testApp4/bin/spring:16:in `require'
  from /home/ec2-user/testApp4/bin/spring:16:in `&lt;top (required)&gt;'
  from bin/rails:3:in `load'
  from bin/rails:3:in `&lt;main&gt;'
  </code></pre>