systemctl & ufw (not just ufw)

[undecidable]

I have recently moved for 14.04 to 18.04. One key difference is systemd.

There seem to be some processes I can run either by entering the command name
or running systemd followed by the unit name.
what is the relation between them?

For example, I run:

>>sudo ufw enable
Firewall is active and enabled on system startup
>>
>>sudo ufw status
Status: active

But if I then do:

>>sudo systemctl status ufw
  ufw.service - Uncomplicated firewall
   Loaded: loaded (/lib/systemd/system/ufw.service; enabled; vendor preset: enabled)
   Active: active (exited) since Wed 2018-07-25 09:31:56 HKT; 8h ago
     Docs: man:ufw(8)
  Process: 363 ExecStart=/lib/ufw/ufw-init start quiet (code=exited, status=0/SUCCESS)
 Main PID: 363 (code=exited, status=0/SUCCESS)

So if I run the ufw cmd, I can enable/disable the firewall.
But this seems to have no relation to the ufw unit managed by sytemctl.

The same thing applies to (say) openvpn.
eg openvpn can be run & managed in the following 2 independent ways:

>>openvpn abc.conf
or
>>systemctl start openvpn@abc

What is systemctl actually doing
with process like ufw where it seems I manage it myself
with the ufw command?

(in processes where there is a separate daemon, eg vnstat and vnstatd,
I understand systemctl would be managing the daemon.)

[#&thj^%]

What is systemctl actually doing
with process like ufw where it seems I manage it myself
with the ufw command?

When I first got introduced to systemd I felt the same way.
that would be a long drawn out answer here is some food for thought: https://www.digitalocean.com/communi...ices-and-units

[undecidable]

Thanks 1fallen.
In fact I have read that, and much more.
I do understand how to use systemctl to manage units etc.

What I don't understand is why there appears to no relation between
running a command and managing that command's unit by systemctl,
as per the examples above.

[steeldriver]

ufw is a bit special imho - it's not really a "service" in the traditional sense (such as running a listening daemon for example), it's just an interface to the kernel's iptables ruleset

If enabled (as a "service") it just runs once on boot to load the rules into the kernel, and then exits - hence

(code=exited, status=0/SUCCESS)

[undecidable]

ah, excellent, clear explanation. Thanks very much steeldriver.

What about openvpn: do you know the difference between running it as a program
>>openvpn /etc/openvpn/abc.conf
and as a systemctl unit:
>>systemctl start openvpn@abc
?

[steeldriver]

Nope sorry - I know nothing about openvpn

[undecidable]

no problem, I think openvpn is likely a simple case of running as a daemon or non-daemon process.
ufw was the greater mystery.
So I'll close this as solved.