vagrant+unicornで立ち上がらない件

vagrantでホストのディスクをマウントしているところに
railsのコードを置いて、unicornを立ち上げたら.sockファイルが作れなくてエラーになった。

config/unicorn.rb の .sock ファイルのパスを /tmp 配下に変えたらちゃんと動いた

/etc/nginx/conf.d/rails.conf

upstream unicorn {
    server  unix:/tmp/unicorn.sock;
}

server {
    listen       8080;
    server_name  localhost;

    access_log  /var/log/nginx/access.log;
    error_log   /var/log/nginx/error.log;

    root /home/vagrant/myapp/public;

    client_max_body_size 100m;
    error_page  404              /404.html;
    error_page  500 502 503 504  /500.html;
    try_files   $uri/index.html $uri @unicorn;

    location @unicorn {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_pass http://unicorn;
    }
}

{rails_root}/config/unicorn.rb

worker_processes Integer(ENV["WEB_CONCURRENCY"] || 3)
timeout 15
preload_app true

listen '/tmp/unicorn.sock'
pid    '/tmp/unicorn.pid'

before_fork do |server, worker|
  Signal.trap 'TERM' do
    puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
    Process.kill 'QUIT', Process.pid
  end

  defined?(ActiveRecord::Base) and
    ActiveRecord::Base.connection.disconnect!
end 

after_fork do |server, worker|
  Signal.trap 'TERM' do
    puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to send QUIT'
  end

  defined?(ActiveRecord::Base) and
    ActiveRecord::Base.establish_connection
end

stderr_path File.expand_path('log/unicorn_stderr.log', ENV['RAILS_ROOT'])
stdout_path File.expand_path('log/unicorn_stdout.log', ENV['RAILS_ROOT'])