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nerves_runtime
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Small, general runtime utilities for Nerves devices
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lib/nerves_runtime/application.ex
defmodule Nerves.Runtime.Application do
@moduledoc false
use Application
require Logger
alias Nerves.Runtime.{Init, Kernel, KV}
alias Nerves.Runtime.Log.{KmsgTailer, SyslogTailer}
@impl true
def start(_type, _args) do
# On systems with hardware random number generation, it is important that
# "rngd" gets started as soon as possible to start adding entropy to the
# system. So much code directly or indirectly uses random numbers that it's
# very easy to block on the random number generator or get low entropy
# numbers.
# On systems with no hardware random number generation, or where rngd is
# not installed, haveged is tried as an alternative.
try_entropy_generator("rngd") || try_entropy_generator("haveged")
target = Nerves.Runtime.target()
children =
[
KV
] ++ target_children(target)
opts = [strategy: :one_for_one, name: Nerves.Runtime.Supervisor]
Supervisor.start_link(children, opts)
end
defp target_children("host") do
[]
end
defp target_children(_target) do
kernel_opts = Application.get_env(:nerves_runtime, :kernel, [])
[
KmsgTailer,
SyslogTailer,
{Kernel.UEvent, kernel_opts},
Init
]
end
defp try_entropy_generator(name) do
path = "/usr/sbin/#{name}"
if File.exists?(path) do
# Launch rngd/haveged. They daemonize themselves so this should return quickly.
case System.cmd(path, []) do
{_, 0} ->
true
{reason, _non_zero_exit} ->
_ = Logger.warn("Failed to start #{name}: #{inspect(reason)}")
false
end
else
false
end
end
end