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.
GZDoom 4.9.0 changed where gzdoom.ini is stored. Starting from 4.9.0, unlike older versions, GZDoom will always prefer the system's user folder and place the INI in
Documents/My Games/GZDoom if no INI is found. This was done to bring handling in line with current guidelines and to make it easier for commecial games that often get installed into a folder without write access. If you still want to store the INI in your game folder you have to create an empty file called GZDoom_portable.ini there before launching. If you still have an old INI in your folder, GZDoom will ask what to do with it, you can either move it to the user folder or convert to a portable install.
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.