Hello,
Thank you for your really appreciated advice. 
I confirm that I misunderstood what "applies to all instances" means.So now 
seems clear. Thanks
But there is something I don't understand.

I have two templates.The second one which is a simple instance of a tail > 
/dev/ttyX under [email protected] renamed it to [email protected] (I don't have 
something which have foo* or bar* as name and previous [email protected] doesn't 
not exist anymore)

I have this [Install] 
Section:[email protected]
systemctl enable [email protected]> Created symlink 
/etc/systemd/system/[email protected] => /etc/systemd/system/[email protected]> 
Created symlink /etc/systemd/system/getty.target.wants/[email protected] => 
/etc/systemd/system/foo@service
Systemctl status [email protected]> Loaded: error (Reason: Unit 
[email protected] to load properly: File Exists)
Systemctl start [email protected] = KO> Failed to start [email protected]: Unit 
[email protected] failed to load properly: File Exists.> See system logs and 
systemctl status [email protected] for details
Systemctl start [email protected] = OK
RegardsHans


    Le jeudi 22 avril 2021 à 20:49:52 UTC+2, Mantas Mikulėnas 
<[email protected]> a écrit :  
 
 On Thu, Apr 22, 2021 at 9:18 PM Hans Gruber <[email protected]> wrote:

Hello,
I am having problems with the aliases and "Alias=' directive related to the 
template service unit.
According to https://www.freedesktop.org/software/systemd/man/systemd.unit.html

> "A template instance may only be aliased by another template instance, and 
> the instance part must be identical. A template may be aliased by another 
> template (in which case the alias applies to all instances of the template). 
> As a special case, a template instance (e.g. "[email protected]") may be a 
> symlink to different template (e.g. "[email protected]"). In that case, 
> just this specific instance is aliased, while other instances of the template 
> (e.g. "[email protected]", "[email protected]") are not aliased. Those rule 
> preserve the requirement that the instance (if any) is always uniquely 
> defined for a given unit and all its aliases."
I have exactly these two cases and requirements and cannot find example.
>  "A template may be aliased by another template (in which case the alias 
>applies to all instances of the template)"

eg: How to create an alias using `Alias=` for a service template [email protected] 
which will have maybe 8 or 16 instances (eg: [email protected] 
[email protected] ..) which will apply to all instances when enabled using eg 
[email protected].


I think you're misunderstanding what "applies to all instances" means. It does 
not give you a super-unit that controls all instances in unison -- rather, it 
gives you a template alias that will provide an alias for *each instance 
individually*.
But one instance is still aliased to one instance. For example, if you alias 
[email protected] => [email protected], then you automatically get [email protected] => 
[email protected], and so on. That's what template aliases do.
If you want to control multiple instances at once, you might be looking for two 
other features:1. Custom target units, which allow you to *start* all instances 
at once;
2. Wildcard support in `systemctl` commands, which allows you to see the status 
of all loaded instances at once (systemctl status "foo@*.service").
-- 
Mantas Mikulėnas  
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