Erlang/OTP 23

This release of Erlang/OTP can be built from source or installed using pre-built packages for your OS or third-party tools (such as kerl or asdf).

Erlang/OTP 23 highlight blog post

docker run -it erlang:23

Potential Incompatibilities

  • Erlang run-time system
    • The deprecated erlang:get_stacktrace/0 BIF now returns an empty list instead of a stacktrace. erlang:get_stacktrace/0 is scheduled for removal in OTP 24.
  • ssl
    • Support for SSL 3.0 is completely removed.
    • TLS 1.3 is added to the list of default supported versions.
  • erl_interface
    • Removed the deprecated parts of erl_interface (erl_interface.h and essentially all C functions with prefix erl_).
  • stdlib
    • In OTP-23.2 a bug fix in uri_string causes decoding of percent-encoded characters to potentially not behave is before.

For a full list see OTP 23.0 - Potential Incompatibilities.


  • OpenSSH 6.5 introduced a new file representation of keys called openssh-key-v1. This is now supported with the exception of handling encrypted keys.
  • Algorithm configuration could now be done in a .config file. This is useful for example to enable an algorithm that is disabled by default without need to change the code.
  • Support for TCP/IP port forwarding, a.k.a tunnelling a.k.a as tcp-forward/direct-tcp is implemented. In the OpenSSH client, this corresponds to the options -L and -R.
  • Support for the middlebox compatibility mode makes the TLS 1.3 handshake look more like a TLS 1.2 handshake and increases the chance of successfully establishing TLS 1.3 connections through legacy middleboxes.
  • Support for key exchange with Edward curves and PSS-RSA padding in signature verification
Language and run-time
  • In binary matching, the size of the segment to be matched is now allowed to be a guard expression (EEP-52)
  • When matching with maps the keys can now be guard expressions (EEP-52).
  • Allow underscores in numeric literals to improve readability. Examples: 123_456_789, 16#1234_ABCD.
  • New functions in the shell for displaying documentation for Erlang modules, functions and types. The functions are:
    • h/1,2,3 – Print the documentation for a Module:Function/Arity.
    • ht/1,2,3 – Print the type documentation for a Module:Type/Arity.
      The embedded documentation is created as docchunks (EEP 48) when building the Erlang/OTP documentation.
  • Our tool chain for building the Windows packages is upgraded with new C++ compiler, Java compiler, OpenSSL libraries and wxWidgets versions. We are now using WSL (the Linux Subsystem for Windows when building) which makes it easier to handle the build environment.
  • The possibility to run Erlang distribution without relying on EPMD has been extended. To achieve this a couple of new options to the inet distribution has been added.
    • -dist_listen false Setup the distribution channel, but do not listen for incoming connection.
    • -erl_epmd_port Port Configure a default port that the built-in EPMD client should return.
  • A first EXPERIMENTAL socket backend to gen_tcp and inet has been implemented. gen_udp and gen_sctp will follow. Putting {inet_backend, socket} as first option to listen() or connect() makes it easy to try this for existing code
  • A new module erpc in kernel which implements an enhanced subset of the operations provided by the rpc module. Enhanced in the sense that it makes it possible to distinguish between returned value, raised exceptions and other errors. erpc also has better performance and scalability than the original rpc implementation. This by utilizing the newly introduced spawn_request() BIF. Also the rpc module benefits from these improvements by utilizing erpc when possible.
  • Scalability and performance Improvements plus new functionality regarding distributed spawn operations.
  • The module pg with a new implementation of distributed named process groups is introduced. The old module pg2 is deprecated and scheduled for removal in OTP 24.