diskimage-builder/diskimage_builder/elements/bootloader/environment.d/10-bootloader-default-cmdline

export DIB_BOOTLOADER_DEFAULT_CMDLINE=${DIB_BOOTLOADER_DEFAULT_CMDLINE:-"nofb nomodeset gfxpayload=text"}
export DIB_BOOTLOADER_SERIAL_CONSOLE=${DIB_BOOTLOADER_SERIAL_CONSOLE:-""}
if [ ! -v DIB_BOOTLOADER_VIRTUAL_TERMINAL ]; then
    # DIB_BOOTLOADER_VIRTUAL_TERMINAL is unset
    export DIB_BOOTLOADER_VIRTUAL_TERMINAL=tty0
else
    # DIB_BOOTLOADER_VIRTUAL_TERMINAL is set to empty string or other value
    export DIB_BOOTLOADER_VIRTUAL_TERMINAL=${DIB_BOOTLOADER_VIRTUAL_TERMINAL}
fi
export DIB_NO_TIMER_CHECK=${DIB_NO_TIMER_CHECK:-"True"}