[systemd-devel] Confusing journal information - journal size

[Anne Mulhern]

----- Original Message -----
> From: "Colin Guthrie" <gmane at colin.guthr.ie>
> To: systemd-devel at lists.freedesktop.org
> Sent: Monday, July 20, 2015 5:38:38 AM
> Subject: Re: [systemd-devel] Confusing journal information - journal size
> 
> David Sommerseth wrote on 17/07/15 14:28:
> > On 17/07/15 13:31, Mantas Mikulėnas wrote:
> >> On Fri, Jul 17, 2015 at 2:13 PM, David Sommerseth <davids at redhat.com
> >> <mailto:davids at redhat.com>> wrote:
> >>
> >>
> >>     Hi,
> >>
> >>     I'm looking through some journals now, and even though I've seen it a
> >>     few times I haven't thought about it until now.
> >>
> >>        systemd-journal[1151]: Runtime journal is using 8.0M (max allowed
> >>                  4.0G, trying to leave 4.0G free of 63.7G available →
> >>                  current limit 4.0G).
> >>
> >>     Could this line be cleaned up so you don't have to look up a man page
> >>     to
> >>     try to figure out what this really means?  Here's my uneducated guess
> >>     and confusion of this line:
> >>
> >>     * Runtime journal is using 8.0M
> >>       - Okay, so currently the journal uses 8MB of disk-space.  No
> >>       problem.
> >>
> >>     * max allowed 4.0G
> >>       - Okay, so the journal should not grow beyond 4GB, makes sense.  No
> >>         problem.
> >>
> >>     * trying to leave 4.0G free of 63.7G available
> >>       - Uhm, what!? So it will grow until there is 4GB left on the
> >>         filesystem?  Not so okay.
> >>
> >>
> >> It chooses the /smallest/ limit, not largest. (Common sense...) For
> >> example, if you had only 5 GB space available, the journal would not
> >> grow beyond 1 GB.
> >>  
> >>
> >>     * current limit 4.0G
> >>       - Ehh ... okay ... so make up your mind, please!  So will the
> >>         journal grow until 4GB or 59.7GB.
> >>
> >>
> >> This *is* it making up its mind: "min(limit 1, limit 2) → resulting limit"
> >>
> >>     But then I looked into /var/log/journal ...
> >>
> >>       # du --si -s /var/log/journal/
> >>       4.3G  /var/log/journal/
> >>
> >>     I do see that both system,journal and user-UID.journal are both 8.4MB,
> >>     and from that I can guess what the log entry tried to tell me with
> >>     "Runtime journal" ... but how is /that/ information useful for me,
> >>     from
> >>     a sys-admin point of view?
> >>
> >>
> >> "Runtime" here means /run, as opposed to persistent in /var. They have
> >> separately configurable limits, since /run is in RAM and /var is usually
> >> on disk. (Though, I'm not entirely sure what purpose the runtime journal
> >> even serves, when /var is available.)
> > 
> > Fair enough.  But you are missing my point.
> > 
> > How this information is presented do require some detail knowledge of
> > the journal.  Don't think like a developer who have poked at the journal
> > code.  Think like a sys-admin who looks through the logs looking for
> > issues.  Then you want to have the answer straight in your face, not
> > needing to go elsewhere to read about these things.  In fact most admins
> > will probably have forgotten what they were going to look for when they
> > move their eyes of the log data.
> > 
> > If it is considered important information, fine.  But present it in a
> > far more understandable way for those who just uses the journal.  Right
> > now, I'm not surprised if most sys-admins read that line as useless
> > gibberish - "Yeah, yeah, journal will waste some space on my drive".
> 
> Yeah, I can't disagree with David. Not sure how best to tidy it up, but
> some rework would definitely be nice.
> 
> Col
> 
> 
> 
> --
> 
> Colin Guthrie
> gmane(at)colin.guthr.ie
> http://colin.guthr.ie/
> 
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After seeing the explanation, the best complete and correct (AFAICT) formulation I could come up with was,

"Runtime journal is using 8.0M (max allowed = min(4.0G, S s.t. total memory(63.7 G) - S = 4.0 G (59.7 G), available memory (16.2 G)) = 4.0G)"

which is compelled to use math speak for clarity and succinctness.

Dunno how happy most sys-admins would be with that.

- mulhern