Blacklisting Unwanted Kernel Modules Like Watchdogs

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Blacklisting Unwanted Kernel Modules Like Watchdogs

PostPosted by natemaia » Sat Jun 10, 2017 6:56 pm

This is gonna be a long one so feel free to back out if you're not interested :lol:
I've tested this on 4 different computers 2 of which are laptops with no issues. With that said You should always exercise caution when changing system files and have a backup
This is not specific to AL but other arch installs as well

I am running AL on reasonably newer hardware (haswell cpu & kepler gpu) and under UEFI. When i reboot on a fully updated fresh install i get two lines stating (a different variation at boot)
kernel: watchdog watchdog0: watchdog did not stop!

then it reboots whether this is a recent change in arch or whether it has always been this way I am not sure. If you use ssd this is less of an issue but on a hdd it can be like 10s.
So I did some research and i found this and
I believe its dependant on what hardware you have but the short story of it is
Many users need this feature due to their system's mission-critical role (i.e. servers), or because of the lack of power reset (i.e. embedded devices). Thus, this feature is required for a good operation in some situations. On the other hand, normal users (i.e. desktop and laptop) do not need this feature and can disable it.

In the context of kernel modules, is a mechanism to prevent the kernel module from loading. This could be useful if, for example, the associated hardware is not needed, or if loading that module causes problems: for instance there may be two kernel modules that try to control the same piece of hardware, and loading them together would result in a conflict.

This is helpful in a number of ways, it allows us to stop kernel modules from loading if not needed. The module may be loaded if another non-blacklisted module depends on it or if it is loaded manually.
You can check the watchdog configuration with
Code: Select all
sudo cat /proc/sys/kernel/watchdog
sudo wdctl
If you get "0" or "/dev/watchdog: No such file or directory" you don't have watchdogs enabled.
wdctl should get you something like this
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Device:        /dev/watchdog
Identity:      iTCO_wdt [version 0]
Timeout:       30 seconds
Timeleft:       2 seconds
KEEPALIVEPING  Keep alive ping reply          0           0
MAGICCLOSE     Supports magic close char      0           0
SETTIMEOUT     Set timeout (in seconds)       0           0

the important part is the Identity: iTCO_wdt that is the module name we need to blacklist
We will also disable the pcspkr module, who needs that these days :lol:

1. Kernel boot parameters
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sudo nano /etc/default/grub
Code: Select all

2. Blacklist folder and config file
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sudo mkdir /etc/modprobe.d
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sudo nano /etc/modprobe.d/modprobe.conf
Copy Paste (this may vary depending on what the Identity of the module listed from wdctl)
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# Do not load the 'pcspkr' module on boot.
blacklist pcspkr

# Do not load the 'watchdog' module on boot
blacklist iTCO_wdt

3. Link to config file in mkinitcpio.conf
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sudo nano /etc/mkinitcpio.conf
Change the FILES section
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# This setting is similar to BINARIES above, however, files are added
# as-is and are not parsed in any way.  This is useful for config files.

4. Rebuild the initramfs (I re - install the current kernel so this part will vary)
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sudo pacman -S linux linux-headers
sudo pacman -S linux-lts linux-lts-headers

5. Rebuild grub
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sudo grub-mkconfig -o /boot/grub/grub.cfg

Reboot, You will have a normal first boot after installing a new kernel.
Now if you run
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sudo cat /proc/sys/kernel/watchdog
sudo wdctl

You should get
wdctl: cannot open /dev/watchdog: No such file or directory
$ cat /proc/sys/kernel/watchdog


Done, You should have a shorter boot/reboot time & shouldnt see any more messages regarding watchdogs.
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Re: Blacklisting Unwanted Kernel Modules Like Watchdogs

PostPosted by womp » Mon Aug 21, 2017 3:19 am

Hi and thanks for this great knowledgeable suggestion!
I have a question though.
"sudo cat /proc/sys/kernel/watchdog" gives "1" but wdctl gives "/dev/watchdog: No such file or directory"!
Strange huh?

Every tweak is needed on my old pc-station!

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Location: Sweden near Halmstad
Running Release: 5.0.0

Re: Blacklisting Unwanted Kernel Modules Like Watchdogs

PostPosted by Brandini » Mon Aug 21, 2017 5:44 am

I get the same as womp
All that I am or seem is but a dream within a dream.
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