replacing rsyslogd in minimal with journald [was Re: systemd requires HTTP server and serves QR codes]

Richard W.M. Jones rjones at
Wed Oct 10 09:12:25 UTC 2012

On Wed, Oct 10, 2012 at 09:54:28AM +0100, Richard W.M. Jones wrote:
> On Wed, Oct 10, 2012 at 09:50:43AM +0200, Björn Persson wrote:
> > Lennart Poettering wrote:
> > > On Tue, 09.10.12 09:09, Chris Adams (cmadams at wrote:
> > > > How do you read this log when the system is not running (e.g.
> > > > mounting filesystems of a drive on another system, running from a
> > > > rescue image, etc.)?
> > > 
> > > journalctl -D <pathtothejournalfiles>
> > 
> > So the rescue system (which might not always be Fedora) must have 
> > journalctl installed. Is the file format stable, or can it break if the 
> > rescue system has a different version of journalctl? Is the format 
> > perchance even documented so that other tools for reading logs could be 
> > written?
> This would be essential for libguestfs tools to parse logs out of
> guests (we do it now by reading /var/log/messages etc which has all of
> the properties you state).

I checked out the code, and it does seem as if the format is intended
to be backwards compatible.  It uses a set of filesystem-like
"compatible" and "incompatible" flags, so presumably a sufficiently
recent journalctl would be able to read any previous version of the
binary file format.

It would be nice to have this confirmed, and indeed enshrined in the
policy of the journal, because it is IMHO essential that the binary
log files will always be readable.


Richard Jones, Virtualization Group, Red Hat
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.

More information about the devel mailing list