For live system analysis, the physical memory source must be one
of the following devices:

  /dev/mem
  /proc/kcore
  /dev/crash

If the live system kernel was configured with CONFIG_STRICT_DEVMEM
or CONFIG_HARDENED_USERCOPY, then /dev/mem cannot be used. 

If the live system kernel was configured without CONFIG_PROC_KCORE,
or if /proc/kcore is non-functional, then /proc/kcore cannot be used.  

The third alternative is this /dev/crash driver.  Presuming that 
/lib/modules/`uname -r`/build points to a kernel build tree or
kernel "devel" package tree, the module can simply be built and
installed like so:

  # make
  ...
  # insmod crash.ko

Once installed, the /dev/crash driver will be used by default for
live system crash sessions.