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

[Dave Howorth]

In the case of a machine that uses an SD card as its primary backing
store, it is desirable to reduce the number of write operations to the
card in order to prolong its life. journald is quite well-behaved in
this regard since it offers the choice of a temporary or permanent
journal and limits the frequency of its writes, except in emergencies.

However, its permanent journal is written under /var/log/journal and
there is no way to configure the path as far as I am aware. I think
this is a problem.

The reason is that on this type of machine people sometimes map
 /var/log to RAM using tmpfs and then perhaps persist the logs using a
program like log2ram. When this is done, journald's emergency writing
capability is lost and crash analysis becomes more difficult.

Of course it is possible instead to redirect the log files of programs
individually to temporary memory using systemd-tmpfiles wherever
needed. But this involves reconfiguring each and every program that
uses /var/log both initially and whenever new programs are installed.
This is tedious not only in quantity but because each program has a
different detailed format of configuration file.

So making /var/log into a tmpfs is a more attractive option. But
ideally the journal would be placed somewhere else in persistent
storage so its contents are available after a crash. This does not seem
to be possible through lack of a config option.

Is my analysis correct? Are there any other ways to resolve this
difficulty? Otherwise, is it possible to consider a log location config
option for journald?

Cheers, Dave