How to find out all Kernel Boot Parameters

how to find out all the available kernel’s command-line parameters (kernel boot parameters)?

It locates in the following file of kernel source code package.

Documentation/admin-guide/kernel-parameters.txt

how to permanently add/change a kernel boot parameter?

Edit file /etc/default/grub or /etc/default/grub.d/xxx.cfg and add the parameter like that (replace aaa=bbb into real parameter)

GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT aaa=bbb"

and update grub

sudo update-grub
sudo reboot

view present kernel boot parameter

cat /proc/cmdline
### or
dmesg | grep "Command line"

online ref:

• https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html
• https://www.kernel.org/doc/html/v4.19/admin-guide/kernel-parameters.html
• https://www.kernel.org/doc/html/v5.10/admin-guide/kernel-parameters.html