6.4. Kernel Boot Parameters

adamherst

The INFO box describes the rd_LVM_LV, rd_NO_LUKS, and rd_NO_DM parameters. I can't find any reference to these in either kernel-parameters.txt or by doing man bootparam. If anyone can point me in the direction of documentation for these parameters it would be appreciated.

Thanks,

Adam

[Edit] I've made a bit of progress. I'm using Ubuntu and the rd module appars to be on Red Hat only. I did a modinfo rd on a CentOS system but none of the above are listed as parameters. Still looking for a pointer to their documentation.

coop

The following has been added to the class:

Note the parameters starting with rd are used only on Red Hat-based systems. Some documentation can be found at https://fedoraproject.org/wiki/Dracut/Options.
***

ALl distros have custom parameters, don't get too carried away. Please note we are
always updating the class content, but we batch the uploads as it is a rather involved process to swap in new course files. So changes may take a week or two to appear.

Thanks for patient reading

adamherst

Hi Jerry,

Thanks for the pointer. I was less concerned about the specifics of these parameters than the process by which, given some arbitrary parameter, I could determine 1) whether it is a valid parameter being used correctly, and 2) how to determine exactly what it does. I had thought that documentation for all boot parameters was supposed to live on the system somewhere. As a result of this exercise, I've concluded that this is not the case and access to resources external to the system is also necessary.

Thanks,

Adam

coop

Actually you do indeed have rather complete documentation on the parameters that
are part of the kernel itself, in a file called "Documentation/kernel-parameters.txt",
which is part of the kernel source. If you have the source it is there, but all distributions have a package with a name like "kernel-doc" that includes it. Or if you google it I'm sure you can find it in a nanosecond. People put a lot of attention into this doc, and no parameter is accepted in the kernel if it is not documented.

Now any parameter passed on the kernel command line that is not understood by the kernel is passed to the first program that runs: init (whether it is the classical /sbin/init or systemd) which then interprets the parameter as it's own. For example, if you just pass "3" that is the am as forcing the system to do "init 3" which means stop at runlevel 3 (no graphics) on sysVinit systems.

You will not find the rd_* parameters, or the LUKS ones etc there; they are being passed to the first init that runs, which is associated with the initramfs. ANd every distro has its own initramfs philosophy. So whether it is you or I, if I want to understand such a parameter I google it There is no secret sauce.

I hope this helps

adamherst

Thanks Jerry. It does help. Here's hoping I always have internet access :-).

Thanks,

Adam