Sorry for automatic completion orthography; here is the real text:
I am starting my system with a rescue cd boot, and I want to consult systemd logs from a previous boot without systemd started.
Journalctl works only when systemd is started.
Is there a work around to consult a previous boot logs without starting systemd?

Hi,

There is the --directory or --file arguments to make journalctl operate on a directory or on a specific journal file instead of the system journal files.

Did you use one of these arguments ?

Hello Ronny,

I don't understand:
are you telling me to use the --directory or --file argument to make journalctl operate on the system journal files as it is its default behavior?

Hmm, you are right.

In this case you need to use the --root option. Since you use a rescue cd boot, you mounted your system in /mnt/ or equivalent, journalctl needs to know where is the root filesystem, so: journalctl --root=/mnt/

If this is not the problem what arguments did you use ? and what error is shown by journalctl exactly ?

No Ronny,
I am chrooted.

Ok, can you provide the error shown by journalctl and the command line you used ?

journalctl looks for the journal files in /var/log/journal/<machine-id>/. If you boot up with a rescue OS that has a different machine ID or a different root it hence won't find any data there.

Hence, make sure:

a) to either chroot to the host OS, and then use journalctl --directory=/var/log/journal/<machine-id>

b) or chroot to the host OS, and then use journalctl -m

b) or to run journalctl --directory=<pathtorootdir>/var/log/journal/<machine-id>

c) or to run journalctl --root=<pathtorootdir> -m

The "-m" swicth merges the journals of all directories in /var/log/journal/*, hence makes it unnecessary to figure out the machine id of the host.