[systemd-devel] How does journald talks to other services?

[Mantas Mikulėnas]

On Fri, Aug 20, 2021 at 2:11 PM Mantas Mikulėnas <grawity at gmail.com> wrote:

> On Fri, Aug 20, 2021 at 2:10 PM Nishant Nayan <nayan.nishant2000 at gmail.com>
> wrote:
>
>> Regarding the below point :
>> c) The service prints to stdout/stderr, but systemd attaches the
>> service's stdout/stderr to a pipe which is read by journald (using
>> sd_journal_stream_fd(3) from libsystemd). See [Service] StandardOutput= in
>> systemd.service(5).
>>
>> I did not see StandardOutput field in [Service] sections of a service
>> file, for example sshd.service, but its logs are visible in journalctl.
>> Is it by default piped to journal and we need to explicitly mention it
>> (StandardOutput=)  only when we want to redirect it somewhere else?
>>
>
> StandardOutput=journal is the default setting.
>

And, actually, sshd doesn't write its messages to stdout anyway – it uses
syslog() via /dev/log; most daemons do.

-- 
Mantas Mikulėnas
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