Ruby exception objects are subclasses of Exception. However, operating systems typically report errors using plain integers. Module Errno is created dynamically to map these operating system errors to Ruby classes, with each error number generating its own subclass of SystemCallError. As the subclass is created in module Errno, its name will start Errno::.

The names of the Errno:: classes depend on the environment in which Ruby runs. On a typical Unix or Windows platform, there are Errno classes such as Errno::EACCES, Errno::EAGAIN, Errno::EINTR, and so on.

The integer operating system error number corresponding to a particular error is available as the class constant Errno::error::Errno.

Errno::EACCES::Errno   #=> 13
Errno::EAGAIN::Errno   #=> 11
Errno::EINTR::Errno    #=> 4

The full list of operating system errors on your particular platform are available as the constants of Errno.

Errno.constants   #=> :E2BIG, :EACCES, :EADDRINUSE, :EADDRNOTAVAIL, ...

System call error module used by webrick for cross platform compatability.

EPROTO

protocol error

ECONNRESET

remote host reset the connection request

ECONNABORTED

Client sent TCP reset (RST) before server has accepted the connection requested by client.