cmdline
Explanation
The file in the /proc filesystem that lists the parameters passed from the bootloader to the kernel is
/proc/cmdline. This file contains a single line of text that shows the command line arguments that were used to boot the kernel. These arguments can include various options, such as the root device, the init process, the console device, and more. The /proc/cmdline file is read-only and cannot be modified at runtime. The parameters in this file are determined by the bootloader configuration, such as GRUB or LILO, and can be changed by editing the corresponding files12.
References: 1: The /proc Filesystem - The Linux Kernel documentation 2: passing bootloader arguments to the kernel - Unix & Linux Stack Exchange