Journalctl

# display logs from current boot
journalctl -b
 
sudo journalctl --since yesterday
journalctl --since "2015-01-10" --until "2015-01-11 03:00"
journalctl --since 09:00 --until "1 hour ago"
 
journalctl -u ssh --since "2019-11-04"
 
journalctl -u nginx.service
 
# journals disc usage
sudo journalctl --disk-usage
 
# show errors
journalctl -p err -b
journalctl -p 3 -xb
 
# show dmesg
journalctl has a --dmesg

Links
https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs
http://0pointer.de/blog/projects/journalctl.html
http://blog.delouw.ch/2013/07/24/why-journalctl-is-cool-and-syslog-will-survive-for-another-decade/