Journalctl

# display logs from current boot
journalctl -b

journalctl --since yesterday

journalctl -u nginx.service

# log disc usage
journalctl --disk-usage

journalctl -p err -b

# 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/