Why my options in the files in sysctl.d are not permanent? I need to run `sudo sysctl -p` often

Question

Following some tutorials to disable ipv6 in my laptop (Ubuntu 16.04), I needed to write in /etc/sysctl.d/99-sysctl.conf the following lines:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

I run sudo sysctl -p and ipv6 is disabled. Fine.

After some time, or if I restart NetworkManager, or reboot my computer, I find in ifconfig that my ipv6 address got back, and I have to run sudo sysctl -p again.

So I cannot understand why my configuration is not definitive and something ignores my kernel parameters at runtime.

After creating 99-sysctl.conf, did you sudo service procps start? — Charles Green, Nov 09 '17 at 16:59
@CharlesGreen will putting it in the sysctl.conf make a difference? — George Udosen, Nov 09 '17 at 17:12
@George I don't remember if I did it on purpose but sysctl.d/99-sysctl.conf and sysctl.conf are identical. So there is no difference. — DdD, Nov 09 '17 at 17:25
@CharlesGreen if I do sudo service procps status I can see that is already active, moreover I can restart it and it fix ipv6 temporarily, until NetworkManager is restarted, then it gets back its ipv6. — DdD, Nov 09 '17 at 17:29
Why would you create /etc/sysctl.d/99-sysctl.conf, if it is identical to /etc/sysctl.conf? The reason for my suggestion of procps can be found in /etc/sysctl.d/README — Charles Green, Nov 09 '17 at 17:43
@CharlesGreen Yes i eliminated one of the two (first one then the other) and I run sudo service procps start, but the behavior remains. The parameters don't look permanent. — DdD, Nov 09 '17 at 22:10
There is an alternate method for disabling ipv6 which worked well for me when I was having some problems https://askubuntu.com/a/337736/283721 — Charles Green, Nov 09 '17 at 22:56
Also, there is an older bug report which I assume would have been fixed by now, and which may be applicable to your system https://serverfault.com/a/494899 — Charles Green, Nov 09 '17 at 23:00
@DdD on my Debian, sysctl.d/99-sysctl.conf is symlinked to sysctl.conf. — pietrodn, May 14 '18 at 06:55

score 4 · Answer 1 · answered Nov 09 '17 at 23:08

There is a reported problem affecting up to Ubuntu 16.04, at https://bugs.launchpad.net/ubuntu/+source/procps/+bug/50093 in which procps.sh which applies the sysctl.conf variable is run too early, and some settings are not applied.

An alternate method for disabling ipv6 is to use a kernel boot parameter as outlines in https://askubuntu.com/a/337736/283721

sudo nano /etc/default/grub

Find the line that contain "GRUB_CMDLINE_LINUX_DEFAULT":

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

Add "ipv6.disable=1" to the boot option, then save your grub file:

GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet splash"

press ctrl+o to save, and ctrl+x to exit nano. Finally, update grub:

sudo update-grub

and reboot to load the changes.

Why my options in the files in sysctl.d are not permanent? I need to run `sudo sysctl -p` often

1 Answers1