[systemd-devel] why log_set_prohibit_ipc() is set in journald

[Mantas Mikulėnas]

On Fri, Aug 27, 2021, 08:52 Nishant Nayan <nayan.nishant2000 at gmail.com>
wrote:

> I have just started to learn journald and in its main function (in
> journald.c) I encountered a function call "log_set_prohibit_ipc(true);"
> In systemd source, I can see the declaration in src/basic/log.h:/*
>
> If turned on, then we'll never use IPC-based logging, * i.e. never log to
> syslog or the journal. We'll only * log to stderr, the console or kmsg
> */void log_set_prohibit_ipc(bool b);
>
> I did not get this because Journald not writing to journal itself by
> default is strange, isn't it?
> What is the reason behind it?
>

My understanding is that the point isn't to prevent logging to journal, but
to prevent logging *through IPC* specifically, i.e. make sure journald
doesn't try to create loopback connections to its own sockets. The journald
daemon is single-threaded, so if it tries to connect to itself, it'll
deadlock.

But also if journald wants to log a critical error (e.g. running out of
space or something like that), then it can't really *rely* on journal still
working...

Afaik, messages written to kmsg will be imported back into the journal
anyway, but that happens asynchronously so it's fine.

>
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