systemd is aliased to /usr/sbin/service, so old sysvinit commands still work:

  $ service nginx status

which should cover your

  if it failed, why , what's the syntax error

For anything more complicated, refer to these cheatsheets:

https://wiki.archlinux.org/title/Systemd#Using_units

https://wiki.archlinux.org/title/Systemd/Journal#Filtering_o...

YMMV. I find systemd a lot easier to work with (I actually started wrapping daemons in proper services instead of sticking everything into nohup or tmux sessions).