RamoopsLogger

An Elixir Logger backend for ramoops linux kernel panic logger. This backend is useful to log oopses and panics into persistent RAM so the logs can survive after a restart. This will enabled debugging of issues after rebooting or rolling back the firmware.

Configuration

RamoopsLogger uses the Linux pstore device driver, so it only works on Linux-based platforms. The official Nerves Projects systems start the pstore driver automatically and you can skip the Linux configuration.

Linux configuration

The most important part of using the RamoopsLogger is ensuring that the pstore device driver is enabled and configured in your Linux kernel. The device driver writes logs to a fixed location in DRAM that is platform-specific. If you are lucky, someone will have determined a good place to store the logs. The official Nerves Project systems all have a small amount of memory allocated for use by the pstore driver. If you are not using Nerves, it's possible that one of the device tree files (for ARM platforms) may be helpful.

One way of testing whether the pstore driver is available is to check whether the /dev/pmsg0 file exists.

Update your Elixir project

Once you're satisfied with the Linux, add ramoops_logger to your project's mix.exs dependencies list.

def deps do
  [
    {:ramoops_logger, "~> 0.3.0"}
  ]
end

Next, update your config.exs to tell the Elixir Logger to send log messages to the RamoopsLogger:

use Mix.Config

# Add the RamoopsLogger backend. If you already have a logger configuration, to add
# RamoopsLogger the only change needed is to add RamoopsLogger to the :backends list.
config :logger, backends: [RamoopsLogger, :console]

IEx Session Usage

To read the last ramoops log to the console run:

iex> RamoopsLogger.dump()

To read the last ramoops log and it to a variable run:

iex> {:ok, contents} = RamoopsLogger.read()

Nerves Automatic Log Check

If you want to have your system check if there is an oops log available, and you are using Nerves, you can add this to your rootfs_overlay/etc/iex.exs file in your firmware project:

if RamoopsLogger.available_log?() do
  IO.puts("Oops! There's something in the oops log. Check with RamoopsLogger.dump()")
end