Systemd journal logs are by default not persistent. They are stored in memory (kernel ring buffer) are /run/log/journal. This means, journal logs are available only from the current boot.
# journalctl --list-boots 0 f27172ee431b4012af52b7623468e2fc Fri 2016-10-21 06:16:53 CDT—Fri 2016-10-21 06:17:22 CDT
Logs from previous boot are not available. However, since journal logs are forward to rsyslog are default, you can still see journal logs from previous boot from /var/log/messages. You will not be able to view logs from previous boots using the journalctl command.
Lets make journal logs persistent.
# mkdir /var/log/journal # systemctl restart systemd-journald # reboot
We now have journal from current boot and previous boot
# journalctl --list-boots -1 f27172ee431b4012af52b7623468e2fc Fri 2016-10-21 06:16:53 CDT—Fri 2016-10-21 06:18:54 CDT 0 9593dfaca170423ea44399e1210da9c8 Fri 2016-10-21 06:19:09 CDT—Fri 2016-10-21 06:19:44 CDT
View journal from current boot
journalctl -b 0
View journal from previous boot
journalctl -b -1
View journal from oldest boot
To reverse the change we made, delete /var/log/journal
# rm -rf /var/log/journal/ # systemctl restart systemd-journald # journalctl --list-boots 0 9593dfaca170423ea44399e1210da9c8 Fri 2016-10-21 06:22:21 CDT—Fri 2016-10-21 06:22:21 CDT