ZDoom's configuration file is an INI file that contains configuration settings for ZDoom.
It is frequently referred to as just zdoom.ini or the ini when the context is clear.
ZDoom's configuration file is named zdoom-<user>.ini, where <user> is the player's username on his or her computer.
Since ZDoom is a portable application, the ini is stored in the same directory as where ZDoom is located, rather than in an %APPDATA% subdirectory.
On Vista and newer Windows systems, folders within the C:\Program Files hierarchy are write-protected. In this case the ini will be stored in %APPDATA% instead.
The .ini extension may be hidden if the default setting of letting the Explorer hide known file extensions is kept.
GZDoom supports portable configuration files: if the engine finds a gzdoom_portable.ini file, it will use that file instead of the user-specific one.
The default location of the configuration file is /home/<user>/.config/zdoom/zdoom.ini.