[systemd-devel] Linux Journal API/client lib

[Kay Sievers]

On Fri, Dec 2, 2011 at 13:59, Rainer Gerhards <rgerhards at gmail.com> wrote:
> as you probably know, I am not a big fan of the journald proposal, but
> that's not the point of my question. I am thinking about how to
> integrate journal data into a syslog logging solution.

You know that the syslog daemon will still see exactly the same log
messages from all clients as it did before, right? The /dev/log file
descriptor that systemd passed to the syslog daemon at startup, will
still carry all the same things regardless of journald's actions.

> So I have a
> couple of questions in regard to accessing the journal. The most
> important one is how to read information from it. From what I have
> read, a client API is planned. I know git has working code, but this
> code is tied into systemd and is not a lib.
>
> So I wonder how a non-systemd app would gain access to journal data.
> Do you actually plan a client library (-ljournal) ?

Yes, a shared library will be provided.

> Or do you plan to
> make this available as a core OS service (and thus via a system call
> interface)?

What do you mean? The journal is just files on disk (or tmpfs), and
the lib can map the file and provide indexed access to it.

> Or anything else? Also, in order to read the complete
> journal, is it necessary to run under the root user or can lower
> privileges be used (and, if so, which)?

All entries are written to individual journals, a separate one for the
system and one for every login uid (user) that submitted entries.
Every login uid can read their own journal, but not directly write it.

All services log into the system journal. The files of the system
journal are owned by a group, you need to be member of that group to
access them.

> These questions were mostly related to the syslogd pulling data from
> the journal to transmit it some remote site (or do some other
> transformation). Now let's assume the contrary, syslogd receives data
> via the network and wants to store it inside the journal. Will there
> be an API provided for that case as well?

Yes, sure, it can just forward things to the journal. Along with what
they log, they will just have some metadata of the forwarder added.

Kay