Hello Colin
Thanks for your response.
Following your reply, I did a test which consisted of the following steps:
1. I ran sudo gedit /etc/default/grub, deleted/removed GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet", ran sudo update-grub and rebooted my machine.
2. Immediately after the reboot, I issued the command nano /proc/cmdline and below is the result:
BOOT_IMAGE=/boot/vmlinuz-4.18.0-0.bpo.1-amd64 root=UUID=[string of alphanumeric characters] ro ipv6.disable=1 quiet
3. Next, I ran the command sudo grep -RF ipv6.disable /etc and below is the result:
/etc/default/grub.ucf-old:#GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet"
/etc/default/grub:GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet"
I am puzzled why ipv6.disable=1 quiet appears in the above results of (2) and (3) despite the fact that I had deleted/removed GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet" from /etc/default/grub.
Regards.
Alan Reding
--------------------------------------------
On Fri, 12/14/18, Colin Watson <cjwatson@debian.org> wrote:
Subject: Re: Bug#916457: grub2-common: Grub refuses to re-enable IPv6 traffic
To: "Alan Reding" <gajUph4pre@yahoo.com>, 916457@bugs.debian.org
Date: Friday, December 14, 2018, 10:56 PM
On Fri, Dec 14, 2018 at 05:23:35PM +0000, Alan Reding
wrote:
> To block IPv6 traffic, I do the following:
>
> 1. Add the following line to /etc/default/grub
>
> GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet"
>
> 2. Run update-grub
>
> 3. In /etc/hosts, add # in front of all lines that
mention IPv6 hosts
>
> 3. Reboot machine
>
> To re-enable IPv6 traffic, I do the following:
[...]
GRUB just passes the stuff in GRUB_CMDLINE_LINUX_DEFAULT
straight
through to the kernel; it has no other involvement in how
the operating
system's networking stack is set up. This could only
possibly be a GRUB
bug if you're finding that update-grub isn't correctly
transferring
GRUB_CMDLINE_LINUX_DEFAULT into /boot/grub/grub.cfg, or if
the kernel
parameters are somehow not actually being passed to the
kernel (which
you can check after boot by looking in /proc/cmdline).
Otherwise, this
cannot possibly be a GRUB bug, and I'd appreciate it if you
could either
close it or figure out some other suitable package to
reassign it to, as
appropriate.
> Method A
>
> 4. Add # in front of the line that contains
> GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet" as in
below:
>
> #GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet"
>
> 5. Run update-grub
>
> 6. In /etc/hosts, remove # from all lines that mention
IPv6 hosts
>
> 7. Reboot machine
>
> Result: IPv6 traffic is still blocked
>
> Method B
>
> 8. In /etc/default/grub, I delete the line
> GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet"
>
> 9. Run update-grub
>
> 10. In /etc/hosts, I ensure that # does not appear in
front of lines that
> mention IPv6 hosts
>
> 11. Reboot machine
>
> Result: IPv6 traffic is still blocked
>
> Method C
>
> 12. In /etc/default/grub, I change the value of
ipv6.disable=0 as in:
>
> GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=0 quiet"
>
> 13. Run update-grub
>
> 14. In /etc/hosts, I ensure that # does not appear in
front of lines that
> mention IPv6 hosts
>
> 15. Reboot machine
>
> Result: IPv6 traffic is NOT blocked. IPv6 traffic is
re-enabled
These symptoms indicate to me that the equivalent of
ipv6.disable=1 is
being set somewhere else *as well*, which causes things to
only work
properly if you explicitly pass the kernel argument
ipv6.disable=0. I'd
suggest looking around in /etc/, perhaps /etc/modprobe.d/.