Hello,

I must admit that I am a bit puzzled by some of your statements :

  ---Steps to Reproduce---
   Steps to follow:
  1. apt-get install linux-crashdump
  2. apt-get install kdump-tools

Step 2 is not required : kdump-tools is a dependency of linux-crashdump so it is installed automatically :

  3. Edit /etc/default/kdump-tools and change the following:
  USE_KDUMP=0 to 1
This is not required. kdump-tools 1:1.5.9-3 does that automatically during installation and you should be prompted to accept it :

  ┌──────────────────────────────────────────────┤ Configuring kdump-tools ├──────────────────────────────────────────────┐   
  │                                                                                                                       │   
  │ If you choose this option, the kdump-tools mechanism will be enabled. A reboot is still required in order to enable   │   
  │ the crashkernel kernel parameter.                                                                                     │   
  │                                                                                                                       │   
  │ Should kdump-tools be enabled by default?                                                                             │   
  │                                                                                                                       │   
  │                                   <Yes>                                      <No>                                     │   
  │                                                                                                                       │   
  └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘   

  4. Change the size of the crash kernel in /boot/grub/grub.cfg to crashkernel=4096M-:4096M
  5. Load the kdump config file: kdump-config load

This will fail with the following :

# kdump-config load
 * no crashkernel= parameter in the kernel cmdline

Which is normal as a reboot is required in order to have the crashkernel parameter taken into account after the reboot.

  6. echo 1 > /proc/sys/kernel/sysrq
  7. echo c > /proc/sysrq-trigger

The hang following this command is normal : as previously stated, a reboot is required otherwise kdump-tools is not loaded.

After the reboot, you should see the following in /var/log/syslog :

Jan 25 11:12:25 XenialS-crashdump kdump-tools[523]: Starting kdump-tools:  * Missing symlink : /var/lib/kdump/initrd.img
Jan 25 11:12:25 XenialS-crashdump kdump-tools[523]: * Creating symlink /var/lib/kdump/initrd.img
Jan 25 11:12:25 XenialS-crashdump kdump-tools[523]: * Missing symlink : /var/lib/kdump/vmlinuz
Jan 25 11:12:25 XenialS-crashdump kdump-tools[523]: * Creating symlink /var/lib/kdump/vmlinuz
Jan 25 11:12:26 XenialS-crashdump kdump-tools[523]: * loaded kdump kernel

To verify the status of kdump you can do :

# kdump-config show
DUMP_MODE:        kdump
USE_KDUMP:        1
KDUMP_SYSCTL:     kernel.panic_on_oops=1
KDUMP_COREDIR:    /var/crash
crashkernel addr: 0x2c000000
current state:    ready to kdump

kexec command:
  /sbin/kexec -p --command-line="BOOT_IMAGE=/vmlinuz-4.3.0-7-generic root=/dev/mapper/VividS--vg-root ro console=ttyS0,115200 irqpoll maxcpus=1 nousb systemd.unit=kdump-tools.service" --initrd=/var/lib/kdump/initrd.img /var/lib/kdump/vmlinuz

Your bug statement shows the following :

  /sbin/kexec -p --args-linux --command-line="root=UUID=e445a093-4593-4e91-bebb-6968483bf2ea ro quiet splash irqpoll maxcpus=1 nousb systemd.unit=kdump-tools.service" --initrd=/boot/initrd.img-4.3.0-5-generic /boot/vmlinux-4.3.0-5-generic

This : --initrd=/boot/initrd.img-4.3.0-5-generic /boot/vmlinux-4.3.0-5-generic indicates that kdump-tools is not properly configured and that your /etc/default/kdump-tools file is the one from a previous version.  I suspect that kdump-tools was improperly configured or that installation of the maintainer's version of the file was refused.

Since 15.10 (Wily), /etc/default/kdump-tools has the following :

KDUMP_KERNEL=/var/lib/kdump/vmlinuz
KDUMP_INITRD=/var/lib/kdump/initrd.img

This was implemented to fix LP: #1496317 which might be the bug that you are encountering.

I suggest that you verify your configuration and run the test again as your description does not describe an actual bug but misconfiguration of kdump-tools