我正在使用Capistrano将一个Ruby on Rails应用程序部署到Linode VPS。我正在使用Unicorn作为应用程序服务器，Nginx作为代理。我的问题是，由于明显的权限问题，我无法启动Unicorn，但我很难追踪到它。
这个Capistrano任务用于启动Unicorn：
task :start, :roles => :app, :except => { :no_release => true } do
run <<-CMD
cd #{current_path} && #{unicorn_bin} -c #{unicorn_config} -E #{rails_env} -D
CMD
end
我得到了一个参数错误（ArgumentError）的返回，指示pid文件的路径不可写。
cap unicorn:start master [d4447d3] modified
* executing `unicorn:start'
* executing "cd /home/deploy/apps/gogy/current && /home/deploy/apps/gogy/current/bin/unicorn -c /home/deploy/apps/gogy/shared/config/unicorn.rb -E production -D"
servers: ["66.228.52.4"]
[66.228.52.4] executing command
** [out :: 66.228.52.4] /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/configurator.rb:88:in `reload':
** [out :: 66.228.52.4] directory for pid=/home/deploy/apps/shared/pids/unicorn.pid not writable (ArgumentError)
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/configurator.rb:84:in `each'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/configurator.rb:84:in `reload'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/configurator.rb:65:in `initialize'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/http_server.rb:102:in `new'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/lib/unicorn/http_server.rb:102:in `initialize'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/bin/unicorn:121:in `new'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/shared/bundle/ruby/1.8/gems/unicorn-4.1.1/bin/unicorn:121
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/current/bin/unicorn:16:in `load'
** [out :: 66.228.52.4] from /home/deploy/apps/gogy/current/bin/unicorn:16
** [out :: 66.228.52.4] master failed to start, check stderr log for details
command finished in 1032ms
failed: "rvm_path=/usr/local/rvm /usr/local/rvm/bin/rvm-shell 'default' -c 'cd /home/deploy/apps/gogy/current && /home/deploy/apps/gogy/current/bin/unicorn -c /home/deploy/apps/gogy/shared/config/unicorn.rb -E production -D'" on 66.228.52.4
最后，这是我Unicorn配置文件（unicorn.rb）相关的部分：
# Ensure that we're running in the production environment
rails_env = ENV['RAILS_ENV'] || 'production'
# User to run under
user 'deploy', 'deploy'
# We will spawn off two worker processes and one master process
worker_processes 2
# set the default working directory
working_directory "/home/deploy/apps/gogy/current"
# This loads the application in the master process before forking
# worker processes
# Read more about it here:
# http://unicorn.bogomips.org/Unicorn/Configurator.html
preload_app true
timeout 30
# This is where we specify the socket.
# We will point the upstream Nginx module to this socket later on
listen "/home/deploy/apps/shared/sockets/unicorn.sock", :backlog => 64
pid "/home/deploy/apps/shared/pids/unicorn.pid"
# Set the path of the log files
stderr_path "/home/deploy/apps/gogy/current/log/unicorn.stderr.log"
stdout_path "/home/deploy/apps/gogy/current/log/unicorn.stdout.log"
我正在使用Capistrano在'deploy'用户和组下进行部署，Unicorn也应该在这个用户和组下运行。
有人知道为什么Unicorn无法写出pid文件吗？任何帮助都将不胜感激！！！
- Mike