named.service or bind9.service or both?

[Jesper Dybdal <jd-debian-user@dybdal.dk>]

I'm running Buster.  I then had a problem with BIND and DNSSEC, so I 
upgraded my bind9 package to the one in buster-backports.

But it seems that this has involved a partial rename of the systemd unit 
from bind9 to named.  So I now have two almost equal systemd units.  And 
named.service includes an "Alias=bind9.service" line, whose exact 
meaning I don't understand.  And named.service includes a "Wants" and a 
"Before" line that bind9.service does not include (details below).

Searching for files named {named,bind9}.service gives:
 28706180      0 -rw-r--r--   1 root     root            0 Apr  3 2016 
/var/lib/systemd/deb-systemd-helper-enabled/multi-user.target.wants/bind9.service
   262273      4 -rw-r--r--   1 root     root          364 Mar 20 2022 
/lib/systemd/system/named.service
 28970007      0 lrwxrwxrwx   1 root     root           33 Jan 15 15:42 
/etc/systemd/system/multi-user.target.wants/named.service -> 
/lib/systemd/system/named.service
 28968976      0 lrwxrwxrwx   1 root     root           33 Apr 10 2016 
/etc/systemd/system/multi-user.target.wants/bind9.service -> 
/etc/systemd/system/bind9.service
 28969163      4 -rw-r--r--   1 root     root          255 Jun  2 2016 
/etc/systemd/system/bind9.service

I suspect that the bind9 service ought to be removed.  Is that correct?  
And I suspect that the first thing to do is "systemctl disable bind9" - 
is that right?  And then perhaps delete the bind9.service file?  But 
what about the "Alias=" line in named.service - does that work if 
bind9.service is removed?

Right now the system is running and the backports nameserver works fine, 
but I wonder if anything will go wrong on the next reboot. And I would 
like to clean up the situation in a way that will not give problems when 
I later upgrade the system to Bullseye.  How do I do that?

Here are the unit files and unit statuses:

> root@nuser:~# systemctl cat bind9
> # /etc/systemd/system/bind9.service
> [Unit]
> Description=BIND Domain Name Server
> Documentation=man:named(8)
> After=network.target
>
> [Service]
> ExecStart=/usr/sbin/named -f -4 -u bind -t /etc/bind
> ExecReload=/usr/sbin/rndc reload
> ExecStop=/usr/sbin/rndc stop
>
> [Install]
> WantedBy=multi-user.target

> root@nuser:~# systemctl cat named
> # /lib/systemd/system/named.service
> [Unit]
> Description=BIND Domain Name Server
> Documentation=man:named(8)
> After=network.target
> Wants=nss-lookup.target
> Before=nss-lookup.target
>
> [Service]
> EnvironmentFile=-/etc/default/named
> ExecStart=/usr/sbin/named -f $OPTIONS
> ExecReload=/usr/sbin/rndc reload
> ExecStop=/usr/sbin/rndc stop
> Restart=on-failure
>
> [Install]
> WantedBy=multi-user.target
> Alias=bind9.service

> root@nuser:~# systemctl status bind9
> ● bind9.service - BIND Domain Name Server
>    Loaded: loaded (/etc/systemd/system/bind9.service; enabled; vendor 
> preset: enabled)
>    Active: active (running) since Sun 2023-01-15 15:47:13 CET; 18h ago
>      Docs: man:named(8)
>  Main PID: 2349 (named)
>     Tasks: 8 (limit: 4691)
>    Memory: 47.0M
>    CGroup: /system.slice/bind9.service
>            └─2349 /usr/sbin/named -f -4 -u bind -t /etc/bind

> root@nuser:~# systemctl status named
> ● named.service - BIND Domain Name Server
>    Loaded: loaded (/lib/systemd/system/named.service; enabled; vendor 
> preset: enabled)
>    Active: failed (Result: exit-code) since Sun 2023-01-15 15:42:14 
> CET; 18h ago
>      Docs: man:named(8)
>   Process: 1412 ExecStart=/usr/sbin/named -f $OPTIONS (code=exited, 
> status=1/FAILURE)
>  Main PID: 1412 (code=exited, status=1/FAILURE)

--
Jesper Dybdal
https://www.dybdal.dk