我正在使用 ruby 2.2.2（运行 ubuntu 16.04）开发 Rails 4.2.3 项目。它工作正常，但在一段时间后重新访问后我无法服务。我试过搜索，但所有情况似乎都没有帮助。这是错误日志：
bigzoo@bigzoo:~/Documents/projects/proj$ rs
=> Booting Puma
=> Rails 4.2.3 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `initialize': could not translate host name "postgres" to address: Name or service not known (PG::ConnectionBad)
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `new'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `connect'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:438:in `new_connection'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:448:in `checkout_new_connection'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:422:in `acquire_connection'
from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:349:in `block …