journalctl

See what the computer is doing

1journalctl -f

Check your own user services:

1journalctl -f

Follow the ssh daemon service

1journalctl -f -u sshd

Find errors since a date

1date=2027-01-01
2journalctl --since=${date} --grep="EXT4-fs error"

Limit the systemd's journal size to 2 gigabytes

1journalctl --vacuum-size=2G
2journalctl --disk-usage

Log the fact that you've installed your own dnsmasq on your system to journalctl, so that you can determine why your system's broken later

1logger "Installed new dnsmasq"
2sudo journalctl -f