[systemd-devel] `Found ordering cycle on _SERVICE_` loops due to `local-fs.target` with `Requires` instead of `Wants` for mounts generated from `/etc/fstab`

[John Florian]

On 2018-04-26 16:04, John Florian wrote:
> On 2018-04-25 04:53, Lennart Poettering wrote:
>> There have been requests in improving the cycle breaking algorithm,
>> but not much has been done in this area, since it's not clear what can
>> be done. Ultimately it's just polishing a broken situation, and
>> the better way out is to fix things properly, i.e. just correct the
>> cycle in the dependencies in the first place.
>
> Having been the author of numerous custom services that are intended 
> to wedge into those provided by systemd/Fedora I've faced resolving 
> these several times and I've never felt all that competent at the 
> task.  Lennart, you were immensely helpful on one occasion by pointing 
> me to `systemctl show FOO` but even then hunting the problem down was 
> far from simple (for me).  I've done the dot/graphviz thing and found 
> it just as useless to me as when I've tried applying it to Puppet's 
> ordering/dependency looping. I'm not blaming those tools (or systemd) 
> because I'm well aware much of the problem is my inability to use them 
> effectively.  The graphs always seem to be overly simple and revealing 
> no problem or overly detailed and obscuring the problem.  Compound 
> that with "an arrow pointing this way means what exactly?"
>
> Is there anything else that could be done to make hunting these loops 
> down easier?  Is there an example of any product that has a similar 
> situation where they excel at helping the developer?  Or are we 
> already there and I just need more practice?  I'm sure part of my 
> struggle is just not encountering these very regularly and integrating 
> into much that I'm only partly familiar with, but the result is the 
> same, trepidation and loathing.

Since I hate to grumble w/o so much as offering any possible 
suggestions... It seems like it might be helpful to have something like 
`systemctl show` but only dumping the properties used for ordering and 
dependencies.  Ideally, only ordering OR dependencies as the case 
warrants and for all units involved, but only those units.