TL;DR: how to access the systemd journal of an offline systemd instance.

So I am migrating some machines over to Ubuntu 16.04 now from the previous LTS version. This means everything is now based on systemd.

Normally I am bootstrapping my machines from a rescue disk of the same version I intend to install, using debootstrap. The reason for this is that for many of my machines I have to run a headless setup.

In a recent case, a machine I am supposed to prepare was booted for me by someone on a remote site, an SSH server was started and a user account configured such that I could log on. That machine had a screen, but due to setting an incompatible mode, the screen remained blank from the point where Ubuntu shows the splash screen. I solved this in the GRUB2 config meanwhile, but the point is, that it was also essentially a headless scenario.

So I set up the machine using debootstrap and tried to boot. The screen remained blank (and either way, I would not have seen the screen myself like in an actual headless installation).

Nothing happened, but the machine could be pinged, but SSH was evidently not running. Puzzling ...

When I rebooted the machine, I was faced with the task to access the systemd journal from the offline machine to figure out what went wrong. I.e. a journal of a systemd instance that wasn't running but of the same version as the one running.

Question: how can I access the systemd journal of a systemd instance that isn't currently running?

# systemd --version
systemd 229

If you can mount the disk of your offline system, you can use the -D or --directory option with journalctl. For example, if you mount the disk to /mnt, you can access its journal with

journalctl -D /mnt/var/log/journal
  • 1
    Hi Jason and welcome to Unix.SE! Thanks for the answer. Unfortunately it comes a little late for my problem back then, but still much appreciated you took the time to answer! Nov 17 '20 at 7:14
  • 1
    I realize a lot of time had passed, and I wanted to answer it because I had the same question and imagine I will have it again some time in the future.
    – Jason
    Nov 18 '20 at 20:18

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