cmdline.txt (Raspberry Pi)

Overview

cmdline.txt is a plain text file used by the Raspberry Pi to pass parameters to the kernel (i.e. the RISC OS ROM) during system boot. The file should be placed in the DOS partition of the boot SD, alongside start.elf and fixup.dat (for more information on these other files, see Software information: Raspberry Pi: Firmware). If it is not present, no parameters are passed.

It should not be confused with config.txt (which is used to supply configuration parameters to the bootloader).

The important thing to remember is that cmdline.txt contains a command line. Only the first line of the file is read, so parameters must be space separated on the first line. For example:

disable_mode_changes disable_gamma

Parameters

At present, the following parameters are available under RISC OS.

disable_gamma

Introduced in July 2018, disable_gamma prevents use of the hardware gamma tables in BCMVideo. Use this parameter if you experience screen blanking problems while running RISC OS 5.25, 5.27 or 5.29.
This parameter is not needed at 5.24/5.26/5.28, as the hardware gamma tables are disabled by default in stable releases of RISC OS.

disable_mode_changes

disable_mode_changes locks the screen pixel resolution to the one chosen at startup. You may want to use this parameter if you are using the “AnyMode” utility to force upscaling of lower-resolution screen modes.
PLEASE NOTE: When using this parameter, you may also need to specify the appropriate hdmi_group and hdmi_mode settings in config.txt. See the documentation page on the Raspberry Pi website for more on hdmi_mode and hdmi_group.