[systemd-devel] logging in RAM and journald configuration issue

[Dave Howorth]

On Tue, 2 Apr 2019 18:47:00 +0200
Lennart Poettering <lennart at poettering.net> wrote:
> On Di, 02.04.19 17:42, Dave Howorth (systemd at howorth.org.uk) wrote:
> 
> > On 2019-03-20 Lennart Poettering wrote:
> >  
> > > On Mi, 20.03.19 18:08, Dave Howorth (systemd at howorth.org.uk)
> > > wrote: 
> > > >
> > > > At present AFAICT the log2ram.service runs
> > > > Before=systemd-journald.service and various other services, so I
> > > > think that aspect is covered.  
> > >
> > > I am not sure what this service does, but if all you want to do is
> > > make changes to /var/log/journal before journald writes there it
> > > should be sufficient to order it before
> > > systemd-journal-flush.service which is nowadays the clear
> > > boundary when journald starts writing to /var.  
> >
> > Sorry for the late reply, but I'm just trying to understand this
> > better. Is systemd-journal-flush.service documented anywhere?  
> 
> It just invokes "journalctl --flush" which is documented here:
> 
> https://www.freedesktop.org/software/systemd/man/journalctl.html#--flush

Thanks. I'm trying to decide the best way to insert this log2ram service
into the system startup order. My handicap is that I'm starting from
zero knowledge of systemd :(

This service needs access to the local filesystem; /var/log in
particular. Ideally it also will startup before any service starts
logging to /var/log, because it needs to rearrange (some may say
pervert!) things so that /var/log is mapped to a ram filesystem and
populated from a persistent record before any arbitrary service starts
reading or writing log files in /var/log. As a special case, it maps
journald's directory back to persistent store, since journald has an
intelligent write strategy. So it needs to start after the /var
filesystem but before any services that use it.

So I'm looking for the appropriate things to put in Before and After
lines for this service.