Detect Linux Runlevel

Marko Rauhamaa marko at pacujo.net
Tue Dec 6 02:47:26 EST 2016


Michael Torrie <torriem at gmail.com>:

> On 12/05/2016 04:37 PM, Marko Rauhamaa wrote:
>> Unfortunately, I am not wholly impressed by the end result. Mogadishu
>> has been replaced by Pyongyang. Some age-old Unix principles have been
>> abandoned without clear justification. For example, I was appalled to
>> find out that a systemd unit can be configured to react on the exit
>> status of a child process of a daemon.
>
> I have yet to see any evidence of this Pyonguang situation.
>
> What is wrong with reacting to the exit status of a daemon's child
> process?

A basic black-box principle is violated. It is surprising, at least.

If I launch a child process, wait it out and ignore its exit status
code, I would think the exit status is meaningless. Not so, because the
Eye is watching.

>> Also, now D-Bus is a fixture for every daemon writer.
>
> But not directly. It need not be a dependency on the part of the
> daemon writer. In fact the daemon writer may now leave out deamonizing
> code entirely if he or she wishes. The systemd api is entirely
> optional for the daemon to use.

Systemd comes with dozens of legacy modes, and it is difficult to learn
what is systemd's "native" daemon type. However, it is evident that
"Type=notify" is it, meaning the daemon communicates with systemd
explicitly (<URL:
https://www.freedesktop.org/software/systemd/man/sd_notify.html>).

That is not necessarily a bad idea. Daemons have traditionally been
lousy at communicating their statuses appropriately. It's just that this
major requirement should be declared openly.

>> The .ini file format was a lousy choice. Why not choose JSON in this
>> day and age?
>
> But why json?

It comes with simple, rigorous, universal syntax. The .ini files don't.
That's why the unit files have brittle ad-hoc syntax.


Marko


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