[Bug 1793369] Re: Ubuntu18.10:ppc64:s390x - Sysrq trigger disabled when writing to /proc/sysrq-trigger

[Thadeu Lima de Souza Cascardo]

The sysrq mechanism allows someone with physical access to the system to
easily cause it to boot by just pressing some keys. That's why the sysrq
default allows only very few commands to be issued. kdump is for real
crashes. kdump testing may require using the sysrq-trigger mechanism,
but that could just as well write to /proc/sys/kernel/sysrq before
causing the crash. In fact, that's just what kdump-tools autopkgtest
does.

echo 1 > /proc/sys/kernel/sysrq
echo c > /proc/sysrq-trigger

So, not a bug here.

** Also affects: systemd (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: systemd (Ubuntu Cosmic)
       Status: New => Won't Fix

** Changed in: linux (Ubuntu Cosmic)
       Status: Triaged => Invalid

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Title:
  Ubuntu18.10:ppc64:s390x - Sysrq trigger disabled when writing to /proc
  /sysrq-trigger

Status in The Ubuntu-power-systems project:
  Triaged
Status in linux package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  New
Status in linux source package in Cosmic:
  Invalid
Status in systemd source package in Cosmic:
  Won't Fix

Bug description:
  == Comment: #0 - Praveen K. Pandey <Praveen.Pandey at in.ibm.com> - 2018-09-19 04:49:39 ==
  ---Problem Description---
   [Witherspoon-DD2.2][Ubu 18.10] [4.18.0-7-generic ] : Sysrq trigger disabled when writing to /proc/sysrq-trigger 

  while  testing kdump trying trigger kdump panic via /proc/sysrq-trigger it failed as : SysRq : This sysrq operation is disabled
  LOG:

  root at test:~# cat /proc/sys/kernel/sysrq 
  176
  root at test:~# echo c > /proc/sysrq-trigger
  root at test:~# dmesg
  [  380.340051] mlx5_core 0000:01:00.1 enp1s0f1: Self test out: status flags(0x2)
  [  389.404239] sysrq: SysRq : This sysrq operation is disabled.
  root at test~# cat /boot/config-4.18.0-7-generic | grep CONFIG_MAGIC_SYSRQ
  CONFIG_MAGIC_SYSRQ=y
  CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x01b6
  CONFIG_MAGIC_SYSRQ_SERIAL=y
  root at test:~# cat /etc/sysctl.conf | grep kernel.sysrq
  #kernel.sysrq=438
  root at test:~# kdump-config show
  DUMP_MODE:        kdump
  USE_KDUMP:        1
  KDUMP_SYSCTL:     kernel.panic_on_oops=1
  KDUMP_COREDIR:    /var/crash
  crashkernel addr: 
     /var/lib/kdump/vmlinuz: symbolic link to /boot/vmlinux-4.18.0-7-generic
  kdump initrd: 
     /var/lib/kdump/initrd.img: symbolic link to /var/lib/kdump/initrd.img-4.18.0-7-generic
  current state:    ready to kdump

  kexec command:
    /sbin/kexec -p --command-line="root=UUID=c0302064-c5a3-49a7-8bd4-402283e6fcbe ro quiet splash nr_cpus=1 systemd.unit=kdump-tools.service irqpoll noirqdistrib nousb" --initrd=/var/lib/kdump/initrd.img /var/lib/kdump/vmlinuz
  root at test:~# 

  Regards
  Praveen

  == Comment: #2 - Praveen K. Pandey <Praveen.Pandey at in.ibm.com> - 2018-09-19 05:16:11 ==
  when i enable  in /etc/sysctl.conf it works  . i append below value in  sysctl.conf

  echo "kernel.sysrq = 1" >> /etc/sysctl.conf

  I think this is should be enable by default  in ubuntu 18.10 as
  earlier ubuntu distro it has , not sure why it got removed as kdump
  mechanism require this .

  Praveen
  Regards

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