在 capistrano 部署脚本中预编译资产后，我立即收到此错误：
Excon::Error::Socket: Too many open files - getaddrinfo (Errno::EMFILE)
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/socket.rb:101:in `getaddrinfo’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/socket.rb:101:in `connect’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/ssl_socket.rb:153:in `connect’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/socket.rb:29:in `initialize’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/ssl_socket.rb:9:in `initialize’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:403:in `new’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:403:in `socket’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:100:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/mock.rb:48:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/instrumentor.rb:26:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:16:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:16:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:16:in `request_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:249:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/idempotent.rb:27:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:272:in `rescue in request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:215:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/idempotent.rb:27:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:272:in `rescue in request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:215:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/idempotent.rb:27:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/middlewares/base.rb:11:in `error_call’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:272:in `rescue in request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/excon-0.55.0/lib/excon/connection.rb:215:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-core-1.43.0/lib/fog/core/connection.rb:81:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-xml-0.1.2/lib/fog/xml/connection.rb:9:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-aws-1.2.1/lib/fog/aws/storage.rb:612:in `_request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-aws-1.2.1/lib/fog/aws/storage.rb:607:in `request’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-aws-1.2.1/lib/fog/aws/requests/storage/put_object.rb:47:in `put_object’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-aws-1.2.1/lib/fog/aws/models/storage/file.rb:219:in `save’
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/fog-core-1.43.0/lib/fog/core/collection.rb:51:in `create’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/storage.rb:208:in `upload_file’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/storage.rb:221:in `block in upload_files’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/storage.rb:219:in `each’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/storage.rb:219:in `upload_files’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/storage.rb:235:in `sync’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/asset_sync.rb:29:in `block in sync’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/asset_sync.rb:51:in `with_config’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/asset_sync/asset_sync.rb:28:in `sync’
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/tasks/asset_sync.rake:5:in `block (2 levels) in <top (required)>'
/home/deployer/au/shared/bundle/ruby/2.4.0/bundler/gems/asset_sync-5d3f776ff2eb/lib/tasks/asset_sync.rake:29:in `block in <top (required)>'
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/webpacker-1.2/lib/tasks/webpacker/compile.rake:40:in `block in <top (required)>'
/home/deployer/au/shared/bundle/ruby/2.4.0/gems/rake-11.3.0/exe/rake:27:in `<top (required)>'
/home/deployer/.rbenv/versions/2.4.0/bin/bundle:22:in `load’
/home/deployer/.rbenv/versions/2.4.0/bin/bundle:22:in `<main>'
我可以看到调用了asset_sync gem，它正在尝试将文件上传到s3。这个问题是一天前开始的，我们还没有增加应该上传到s3的文件数量。
调试时我们可以做些什么来限制范围？我们可以通过查看这个日志输出来排除一些东西吗？是这个特定进程（预编译 rake 任务）打开了太多文件吗？
在发生此错误时，我们如何调试进程打开了哪些文件？