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
 
journalctl --disk-usage
 
# Clear systemd journals older than X days
journalctl --vacuum-time=31d
 
# Clear systemd journals if they exceed X storage
journalctl --vacuum-size=1G
 
# show NetworkManager logs
journalctl -u NetworkManager
 
# show cron logs
journalctl -f -u cron