You can set the :truncate option to an appropriate value:

:truncate - the maximum message size to be logged (in bytes). Defaults to 8192 bytes. Note this configuration is approximate. Truncated messages will have " (truncated)" at the end. The atom :infinity can be passed to disable this behavior.

I have exact same need (to see which file and line blows up), my solution is inspecting inside terminate/2 callback.

# You will know it when you need it
def terminate({_, trace}, _socket) do
  IO.inspect(trace, label: "terminate trace")
end

It will show file and line number without data log.

Unfortunately, the truncate setting has no effect, I’ve already tried that. Here’s my logger config:

config :logger,
  backends: [
    :console,
    {LoggerFileBackend, :error},
  ]
config :logger, :error,
  path: "/home/me/logs/scraper/error.log",
  level: :error,
  handle_otp_reports: true,
  handle_sasl_reports: true,
  truncate: :infinity

config :logger, :console,
  handle_otp_reports: true,
  handle_sasl_reports: true,
  level: :debug,
  truncate: :infinity

Both console, and the file have the log messages truncated.

Am I perhaps missing something?