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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. – trismarck 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. – Mohsen Pahlevanzadeh 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

3 Answers

up vote 3 down vote accepted

One way to do that is to list the available parameters for that module and finally, if your parameter is a valid one, check to see whether it has been enabled/disabled depending on what you specified on your boot line.

Example:

If I added libahci.ignore_sss=1 to my boot line and wanted to check whether it's been taken into account, I could run:

ls /sys/module/libahci/parameters/

which returns:

ahci_em_messages  ignore_sss  skip_host_reset

so my parameter is a valid one. Then it's only a matter of checking its value:

cat /sys/module/libahci/parameters/ignore_sss 

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EDIT: note that the above only works for loadable kernel modules. For built-in modules you have to specify the path to the driver, in your particular case atkbd:

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

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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'. – trismarck Sep 19 '12 at 17:13
@trismarck - I updated my post, hth. – don_crissti Sep 19 '12 at 17:26
This is great, thanks very much. – trismarck Sep 19 '12 at 17:47
up vote 1 down vote

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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up vote 0 down vote

/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'. – trismarck Sep 19 '12 at 13:18
This answer is totally irrelevant to the question then. – Marco Sep 19 '12 at 13:20

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