systemctl and journalctl Cheat Sheet

systemctl status nginx              # state, recent log lines
sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx        # stop, then start
sudo systemctl reload nginx         # re-read config, without a restart
sudo systemctl reload-or-restart nginx

sudo systemctl enable nginx         # start at boot
sudo systemctl enable --now nginx   # and start it now
sudo systemctl disable nginx
sudo systemctl disable --now nginx  # and stop it now
systemctl is-enabled nginx
sudo systemctl mask nginx           # forbid it from starting at all
sudo systemctl unmask nginx

systemctl --failed                     # what failed?
systemctl list-units --type=service    # loaded services
systemctl list-units --state=running --type=service
systemctl list-unit-files --type=service   # all, with enabled/disabled
systemctl is-active nginx              # for scripts
sudo systemctl reset-failed nginx      # clear a "failed" state
systemctl status 812                   # which unit does this PID belong to?

systemctl cat nginx                    # the unit, and every override
systemctl show nginx -p Restart,User,ExecStart   # effective settings
sudo systemctl edit nginx              # add an override (survives upgrades)
sudo systemctl edit --full nginx       # edit a full copy
sudo systemctl revert nginx            # remove your overrides
sudo systemctl daemon-reload           # after changing a unit file by hand

systemctl is-system-running            # running, or degraded?
systemctl get-default                  # multi-user or graphical?
sudo systemctl reboot
sudo systemctl poweroff
systemd-analyze blame                  # what made boot slow?
systemd-analyze verify myapp.service   # check a unit for mistakes

systemctl list-timers --all            # when did each run, and when's next?
sudo systemctl enable --now backup.timer
sudo systemctl start backup.service    # run the job now
journalctl -u backup.service -n 50
systemd-analyze calendar 'Mon *-*-* 03:00'   # check a schedule

journalctl -u nginx                    # one service
journalctl -u nginx -f                 # follow
journalctl -u nginx -n 50 --no-pager   # last 50 lines, for pasting
journalctl -xeu nginx                  # the end, with explanations
journalctl -b                          # since this boot
journalctl -b -1                       # the previous boot
journalctl -k                          # kernel messages only

journalctl --since "1 hour ago"
journalctl --since "2026-11-06 09:00" --until "2026-11-06 10:00"
journalctl --since today -u nginx -u php8.3-fpm     # several units
journalctl -p err -b                   # errors and worse, this boot
journalctl -g 'timed out' -u nginx     # search by text (a regex)
journalctl _PID=812                    # one process
journalctl -o json-pretty -n 1         # every field of one entry
journalctl -o cat -u nginx             # only the messages

journalctl --disk-usage
sudo journalctl --vacuum-size=500M     # shrink to 500 MB
sudo journalctl --vacuum-time=14d      # keep two weeks

systemctl --user status myapp
systemctl --user enable --now myapp
journalctl --user -u myapp
sudo loginctl enable-linger alex       # keep them running after logging out