Configuring the default logger through a config file

Koszal

The bash script below generates and umbrela project (mix new --umbrella logcfg) and then an app (mix new demo). It then creates a task and adjusts config for the :default logger. Finally, everything is compiled and the generated task runs. (mix hello). Despite setting :type and :filesync_repeat_interval in the config, the logger still sees the default values:

19:07:52.772 [warning] config.type :standard_io
19:07:52.773 [warning] config.type :no_repeat

Why?
Elixir 1.15.7 (compiled with Erlang/OTP 26)

Koszal

#!/bin/bash

mkdir /tmp/logger-$$
cd    /tmp/logger-$$

mix new --umbrella logcfg
cd logcfg

dsn=`pwd`

cd $dsn/apps
mix new demo

mkdir -p $dsn/apps/demo/lib/mix

cat <<TASK > $dsn/apps/demo/lib/mix/hello.ex
defmodule Mix.Tasks.Hello do
  use Mix.Task
  require Logger

  def run(_) do
    :logger.get_handler_config(:default) |> IO.inspect()

    {:ok, lcfg} = :logger.get_handler_config(:default)
    Logger.warning( "config.type #{ inspect(lcfg[:config][:type]) }" )
    Logger.warning( "config.filesync_repeat_interval #{ inspect(lcfg[:config][:filesync_repeat_interval]) }" )
  end
end
TASK

cat <<CONFIG >> $dsn/config/config.exs
config :logger, :default,
  config: [
    type: :standard_error,
    filesync_repeat_interval: 5000
  ]
CONFIG

cd $dsn
mix compile
mix hello
pwd

8 comments

#logger #config

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2024-06-11 15:14:07 UTC

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cmo

Do you need to configure default_handler, not default?

Here is a working config for file logging:

config :logger, :default_handler,
  config: [
    filesync_repeat_interval: 5000,
    file_check: 5000,
    max_no_bytes: 10_000_000,
    max_no_files: 5,
    compress_on_rotate: false,
    file: ...
  ]

Post #1

Koszal

I had tried that before (and a few other things) and it still said

06:42:06.040 [warning] config.filesync_repeat_interval :no_repeat

So you either have an older Elixir version (there were changes to the logging mechanism), or it does not work in the context of the task, or there is something else I don’t understand…

Have you run the bash script after changing default to default_handler? What does it print?

Post #2

cmo

I’m in 1.16.3 and sorry but I won’t be running your bash script.

Post #3

hauleth

If you are using OTP 24+ and you aware of the consequences, then you can run logger:reconfigure/0 as part of your startup script. In general default handler is only partially configurable after it started.

Post #4

Koszal

You seem to apply I need some black magic whereas in fact I just want to figure out how to configure basic properties of the logger.

I have followed Elixir documentation at

It tells you to put the settings in config/config.exs and gives a snippet of code.

My current config is

config :logger, :default_handler,
  config: [
    file: ~c"/home/kos/elixir-demo.log",
    type: :standard_error,
    filesync_repeat_interval: 4000,
    file_check: 5000,
    max_no_bytes: 10_000_000,
    max_no_files: 5,
    compress_on_rotate: true
  ]

I have also tried config at the application level:

config :demo, :logger, [
  {:handler, :file_log, :logger_std_h, %{
     config: %{
       file: ~c"/home/kos/elixir-demo.log",
       type: :standard_error,
       filesync_repeat_interval: 300,
       file_check: 5000,
       max_no_bytes: 10_000_000,
       max_no_files: 5,
       compress_on_rotate: true
     },
     formatter: Logger.Formatter.new()
   }}
]

Nothing seems to affect the logging. The log file is not created, messages appear on stdout (rather than stderr), etc.

Post #5