How To Blacklist A Device Driver (sysemd)

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Hi,

how can a specific device driver in CentOS 7 be blacklisted, so that it doesn’t load at boot time? We have Infiniband adapters which are not completely supported by CentOS and we want to silence the error messages for the time being.

I tried with the files

/etc/modprobe.d/blacklist
/etc/modprobe.d/blacklist.conf

and with entries

mlx5_core
mlx5_ib

blacklist mlx5_core
blacklist mlx5_ib

install mlx5_core /dev/null
install mlx5_ib /dev/null

all found on different websites.

None of these entries helps. mlx5_core and mlx5_ib are still loaded and the system is flooded with error messages.

Cheers frank

5 thoughts on - How To Blacklist A Device Driver (sysemd)

  • The “blacklist” entries prevent a module being loaded by its alias
    (typically a PCI ID), but not from being loaded if something explicitly loads it by module name.  Most likely, those modules are included in your initrd.

    I’d suggest using the entries described above, and editing grub.conf to add arguments to the kernel command line:
        rd.driver.blacklist=mlx5_core rd.driver.blacklist=mlx5_ib
    … then rebuilding your initrd using “dracut –force”

  • Thanks for the hint. However as this should only be a temporary measure and needs to be done on ca. 100 hosts I’m not sure if we want to go through the hassles. Deploying a textfile is no problem, but creating new initrds for differing hardware….

    frank

  • Well, use “lsinitrd /boot/” to confirm that the driver is actually part of yours.  If so, I suspect you’ll at least need to add the kernel args.  At a minimum, that’d require distributing a modified
    /etc/default/grub and running “grub2-mkconfig -o /etc/grub2-efi.cfg”. 
    It might not require any other changes…

  • Frank Thommen wrote:

    They are probably being loaded via the initramfs at boot time – i.e. before the real root is mounted (where the blacklist entries exist)

    I believe you can either add ‘rd.driver.blacklist=‘ to the grub2 boot cmdline – or generate a new initramfs (using ‘dracut -f -v’ –
    make a copy of your current initramfs first) – as this should pull in entries in /etc/modprobe.d/

    James Pearson



  • Having had to blacklist things like this in the past, it has been my experience that James is correct. If the driver is available in the existing initrd (created before the updates to the blacklists), then the driver WILL be loaded prior to the blacklists being read. For me I found two solutions that worked:
    1) (re)install a new kernel after blacklist creation (which causes an dracut run with all the correct parameters)
    2) create the blacklists, then workout the correct dracut parameters and run it.

    obviously from the point of avoiding research time, doing a boot into an _older_ kernel,
    ‘yum remove kernel-currentversion; yum update kernel’ is easier, but once you figure out how to tell Dracut to use it’s usual parameters for each machine you can avoid the time of doing the extra reboot on a bunch of machines. It has been ~4 years since I looked at this so I don’t remember how to automate using the right options per machine. Or you could wait for the next CentOS 7 kernel update…Unfortunately the CVE’s for the 6 kernel that just came out were all fixed in the 7 kernel back in October, so I have no expectation of a new 7 kernel anytime soon.

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