This document aim to list all deprecated functionality in Erlang/OTP. It was introduced as of OTP 22, and have not yet been updated with all old deprecations. Deprecations made in other parts of the documentation are of course still valid. For more information regarding the strategy regarding deprecations see the documentation of Support, Compatibility, Deprecations, and Removal.
The old legacy erl_interface library (functions with prefix erl_) is deprecated as of OTP 22. These parts of erl_interface has been informally deprecated for a very long time. You typically want to replace the usage of the erl_interface library with the use of the ei library which also is part of the erl_interface application. The old legacy erl_interface library has also been scheduled for removal.
The format of "System Events" as defined in the man page for sys has been clarified and cleaned up. Due to this, code that relied on the internal badly documented previous (before this change) format of OTP's "System Events", needs to be changed.
In the wake of this the function sys:get_debug/3 that returns data with undocumented and internal format (and therefore is practically useless) has been deprecated, and a new function sys:get_log/1 has been added, that hopefully does what the deprecated function was intended for.
New time functionality and a new time API was introduced. For more information see the Time and Time Correction chapter in the ERTS User's guide and specifically the Dos and Donts section on how to replace usage of erlang:now().