I’ve spent many hours on this today, testing researching & coming to some degree of understanding. I found:
1. Creating a .conf file in /etc/sysctl.d/ did not work.
If you run ‘sysctl --system’ it will show you the order that the settings were applied. The naming is important. I found that in order to override settings in /usr/lib/sysctl.d/50-default.conf, my configuration file in /etc/sysctl.d/ needed to be named something like 80-custom.conf (or similar) so that it was processed after the default configuration…
linux-kgxs:/home/dean # sysctl --system
* Applying /boot/sysctl.conf-4.4.79-19-default ...
kernel.hung_task_timeout_secs = 0
kernel.msgmax = 65536
kernel.msgmnb = 65536
kernel.shmmax = 0xffffffffffffffff
kernel.shmall = 0x0fffffffffffff00
* Applying /usr/lib/sysctl.d/50-coredump.conf ...
kernel.core_pattern = |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %e
* Applying /usr/lib/sysctl.d/50-default.conf ...
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.promote_secondaries = 1
net.ipv4.conf.all.promote_secondaries = 1
net.ipv6.conf.default.use_tempaddr = 1
fs.inotify.max_user_watches = 65536
kernel.sysrq = 184
dev.cdrom.autoclose = 0
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
kernel.kptr_restrict = 1
* Applying /etc/sysctl.d/80-custom.conf ...
kernel.sysrq = 252
* Applying /etc/sysctl.d/99-sysctl.conf ...
net.ipv4.ip_forward = 0
net.ipv6.conf.all.forwarding = 0
* Applying /etc/sysctl.conf ...
net.ipv4.ip_forward = 0
net.ipv6.conf.all.forwarding = 0
linux-kgxs:/home/dean # cat /proc/sys/kernel/sysrq
252