Autorun is a common feature of many first-person shooter games, allowing the player character to constantly move at a higher than normal speed without requiring constant input from the player. While the Doom engine did not officially support this, ordinarily requiring the player to hold down the SHIFT key or a dedicated mouse or gamepad button to run, it has been added by most source ports and can usually be toggled on or off by pressing a key on the keyboard. CAPSLOCK is commonly used for this purpose, though not without difficulties on some platforms where this key is treated specially.
Support through joyb_speed
The Doom engine inadvertently supports autorun via a glitch in the configuration file system. Because variables specified in the configuration file are not range checked in any fashion when they are read into the game's memory at startup, it is possible to set the gamepad button used for running, which is called joyb_speed in the configuration file, to a value outside the normal range of 0 to 3, causing the game to believe that button is being held down. See the additional settings section of the configuration file article for more information.