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In the grub.conf configuration file I can specify command line parameters that the kernel will use, i.e.:

kernel /boot/kernel-3-2-1-gentoo root=/dev/sda1 vga=791 plasticDuck

After booting up a given kernel, is there a way to tell if all parameters were passed 'correctly'?

I.e. there is no plasticDuck kernel parameter, but:

dmesg | grep plasticDuck

only returns:

Kernel command line: root=/dev/sda1 vga=791 plasticDuck

(no error)

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Not sure I understand the question entirely. You want to know if a parameter was actually taken into account/acted on? (i.e. in your example, you'd like to know that plasticDuck was ignored since the actual kernel parameter is plasticPenguin, i.e. you got a typo.) – Mat Sep 19 '12 at 13:03
@Mat Exactly something like that. The background of the story: I have found the 'atkbd.softraw' kernel parameter and I this parameter works for kernels 2.6.x, but my kernel version is 3.2.12. And I'm wondering if I can still use that parameter or not. – colemik Sep 19 '12 at 13:14
Ok, understood. Don't know of anything generic though, sorry. – Mat Sep 19 '12 at 13:16
vga parameter is deprecated! but works for backward compatibility. – PersianGulf Sep 19 '12 at 13:49
Valid? Looks like you just want to tell if it's actually used by kernel? If your see it in /proc/cmdline, it's being used, but whether it effects is unknown. – warl0ck Sep 19 '12 at 14:09
up vote 3 down vote accepted

I don't think there's a command that lists built-in modules parameters and their values. If you know the path to the driver files you could list the parameters for that module e.g. if you used ipv6.autoconf=0 as a kernel boot parameter you could run:

ls -1 /sys/module/ipv6/parameters/

and then, if the specified parameter is in the list (i.e. it is valid), check its value:

cat /sys/module/ipv6/parameters/autoconf 

Or, in your particular case - atkbd:

cat /sys/bus/serio/drivers/atkbd/serio0/softraw

As per gilles post, for loadable modules you could use modinfo to list specific parameters and possible values but that doesn't work for built-in modules (although there have been attempts to add support for built-in modules):

modinfo ipv6
modinfo: ERROR: Module ipv6 not found.
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Is there any way I can apply this procedure to a built-in kernel module? (I can't switch the atkbd module so it is compiled as a module). By a built-in kernel module I mean a module that is 'hard-compiled' into the kernel - I can't even disable it (or I don't know how). And thanks for the 'module' part. I didn't know I can pass parameters to kernel modules, in comparison to the kernels 'core'. – colemik Sep 19 '12 at 17:13
This is great, thanks very much. – colemik Sep 19 '12 at 17:47

/proc/cmdline file contains the parameters which were passed to the kernel.

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Does this mean that plasticDuck does not show up in cmdline? – Marco Sep 19 '12 at 13:16
@Marco it still shows up in cmdline, even if 'not valid'. – colemik Sep 19 '12 at 13:18
This answer is totally irrelevant to the question then. – Marco Sep 19 '12 at 13:20

You can't tell whether a parameter is valid. Parameters passed to the kernel are also passed to modules (in addition to the parameters passed when loading the module itself), and maybe a module that you haven't loaded yet will understand this parameter.

The modinfo command lists the parameters that a module understands. You can see the parameters of a loaded module in /sys/module/$module_name/parameteres/. I am not aware of anything similar for the kernel itself.

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