Thanks Deano & Gerry
You can define the necessary (eg kernel.sysrq = 1) in /etc/sysctl.conf, or a .conf file in the /etc/sysctl.d/ directory
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. Given i had successfully previously done in this Maui Linux prior to my conversion months ago to oS TW, today i “borrowed & repurposed” my old Maui file file; /etc/sysctl.d/10-magic-sysrq.conf:
# The magic SysRq key enables certain keyboard combinations to be
# interpreted by the kernel to help with debugging. The kernel will respond
# to these keys regardless of the current running applications.
#
# In general, the magic SysRq key is not needed for the average Ubuntu
# system, and having it enabled by default can lead to security issues on
# the console such as being able to dump memory or to kill arbitrary
# processes including the running screen lock.
#
# Here is the list of possible values:
# 0 - disable sysrq completely
# 1 - enable all functions of sysrq
# >1 - enable certain functions by adding up the following values:
# 2 - enable control of console logging level
# 4 - enable control of keyboard (SAK, unraw)
# 8 - enable debugging dumps of processes etc.
# 16 - enable sync command
# 32 - enable remount read-only
# 64 - enable signalling of processes (term, kill, oom-kill)
# 128 - allow reboot/poweroff
# 256 - allow nicing of all RT tasks
#
# For example, to enable both control of console logging level and
# debugging dumps of processes: kernel.sysrq = 10
# #
# 3/9/17: openSUSE Tumbleweed default in /proc/sys/kernel/sysrq = 184
#However 184 only enables S U B. By my deduction to enable REISUB, atop existing TW options, need 252.
kernel.sysrq = 252
Unfortunately after rebooting, despite that new file, /proc/sys/kernel/sysrq remained at 184, & in tty i confirmed that R E I remained disabled, with only S U B being enabled & functional.
2. Conversely, this is very successful: adding this instead to* /etc/sysctl.conf:*
#
# Magic SysRq REISUB:
# 3/9/17: openSUSE Tumbleweed default in /proc/sys/kernel/sysrq = 184
#However 184 only enables S U B. By my deduction to enable REISUB, atop existing TW options, need 252.
kernel.sysrq = 252
After rebooting, /proc/sys/kernel/sysrq now showed 252, & in tty i confirmed that each of R E I S U B is now enabled & functional.
3. FYI, based on today’s research & testing, this pic from my little working spreadsheet shows how i deduced my 252 :
https://paste.opensuse.org/images/35014126.png