unicornの起動がうまくいかない

###前提・実現したいこと
vagrant(CentOS6)上のRailsアプリケーションをunicorn+nginxで構築したサーバで動かしたい。
別の環境では動くことが確認できているのですが、現在うまく立ち上がらずに困っています。

###発生している問題・エラーメッセージ

$ rake unicorn:start
bundle exec unicorn_rails -c /vagrant/config/unicorn/development.rb -E development -D
master failed to start, check stderr log for details
rake aborted!
Command failed with status (1): [bundle exec unicorn_rails -c /vagrant/conf...]
/vagrant/lib/tasks/unicorn.rake:16:in `block (2 levels) in <top (required)>'
Tasks: TOP => unicorn:start
(See full trace by running task with --trace)

ログ

I, [2016-09-28T12:30:47.815853 #7554]  INFO -- : Refreshing Gem list
I, [2016-09-28T12:30:55.425176 #7554]  INFO -- : unlinking existing socket=/tmp/unicorn.sock
F, [2016-09-28T12:30:55.425724 #7554] FATAL -- : error adding listener addr=/tmp/unicorn.sock
bundler: failed to load command: unicorn_rails (/usr/local/rbenv/versions/2.2.5/bin/unicorn_rails)
Errno::EPERM: Operation not permitted @ unlink_internal - /tmp/unicorn.sock
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:113:in `unlink'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:113:in `rescue in bind_listen'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:107:in `bind_listen'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:231:in `listen'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `block in bind_new_listeners!'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `each'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `bind_new_listeners!'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:130:in `start'
  /usr/local/rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/unicorn-5.1.0/bin/unicorn_rails:209:in `<top (required)>'
  /usr/local/rbenv/versions/2.2.5/bin/unicorn_rails:23:in `load'
  /usr/local/rbenv/versions/2.2.5/bin/unicorn_rails:23:in `<top (required)>'

/config/unicorn/development.rb

# -*- coding: utf-8 -*-
@app_path = '/vagrant'
worker_processes Integer(ENV["WEB_CONCURRENCY"] || 3)
timeout 150
preload_app true  # 更新時ダウンタイム無し

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

super userでrake unicorn:startすると、通るのですが502 Bad Gatewayとなってしまいます。
何かヒントでもいただければ幸いです。よろしくお願いいたします。