I forget about this all the time, so here are some commands I often use for debugging/devops
systemctl list-units systemctl status unit_name service unit_name start|stop|status
Some apps have logs in a directory (often /var/log), some can be read directly using
journalctl -u unit_name --since "2019-12-04 00:00:00" --until "2019-12-05 23:00" journalctl -u unit_name --follow
$ netstat -ntlp
ulimit -n lsof -p 13 | wc -l lsof -p $(pgrep ds_proxy) | wc -l
htop is pretty useful, it’s interesting to see where the numbers come from under the hood: htop explained.