Journald

output since booting:

journalctl -b

Follow:

journalctl -f

Keep an eye on sshd service:

journalctl -b -f -l -u sshd

Examples:

journalctl -b --system
journalctl -b --user

journalctl --since=yesterday

journalclt -b _PID=1
journalclt -b _UID=1001
journalclt -b /usr/bin/sudo
journalctl KERNEL_DEVICE=+scsi:0:0:0:0

-x -> extra info

To monitor the output of dmesg:

# journalctl -kf

or

# dmesg -wH