How do I read logs from the previous boot?

The quick answer

journalctl -b -1 shows journal entries from the previous boot, provided those entries were retained.

journalctl -b -1

What's going on?

journalctl -b -1 shows journal entries from the previous boot, provided those entries were retained.

Understanding the underlying mechanism makes troubleshooting much easier than memorising a command in isolation.

Dig a little deeper

List available boots with journalctl --list-boots. Persistent journals usually live in /var/log/journal; volatile journals may disappear on reboot.

Hands-on commands

Try these in a suitable test environment. Read each command before running it, especially if you have elevated privileges.

journalctl --list-boots
sudo journalctl -b -1 -p warning
sudo journalctl -u ssh -b -1