Discover linux kernel boot options

Is there a cross-distribution way to know the boot parameters supplied to the kernel?

Assuming you're asking about the options passed to the current-running kernel?

1. If the /proc filesystem is in use, /proc/cmdline tells you exactly what options were passed to the kernel.

   $ cat /proc/cmdline  
   root=UUID=3630dd43-f9f9-40b1-8a5f-72c13f2b309c ro quiet splash
   

2. If there's no /proc filesystem, you can get an idea by finding the current kernel's entry in grub.conf or other bootloader configuration. (Use "uname -r" to see what kernel is currently running.) This won't tell you what WAS used to boot the current kernel, just what is NORMALLY used.

I'm guessing you're talking about the Linux Kernel, so there is a set of standard parameters which it accepts.