How do i set the default simulation run length to be less than 10S


i’m doing some simulation mode runs and want to change the default run length to be less than the default 10 seconds. i know this is possible because it’s described in the docs (here and here) but i am having trouble interpreting exactly what i am supposed to change.

i’ve tried the two things in the screenshots but they both fail.

i appreciate this is simply a case of me not knowing how to read the docs properly so hopefully i can learn something here! for example, in this syntax…

flow.cylc[runtime][<namespace>][simulation]default run length

what exactly does [<namespace>] refer to?

let’s say i have a workflow with like (probably wrong syntax but you get the idea)…

R1 = foo => bar
PT1M => foo[-PT1M] 

does [<namespace>] refer to foo and bar respectively? or can i set a global new simulation time of, say, 2s?

thanks for any tips and tricks as per usual!


The single-line shorthand notation:


corresponds to this in the flow.cylc format:


So <namespace> can be any task or family name (including root if you want to set the simulated run-length for all tasks at once).

For future reference, it’s defined in the config reference section of the docs:

(It’s called a “namespace” for somewhat valid technical reasons, and to avoid having to say “task or family name” all the time).

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Yes, you can do this like so

            default run length = PT2S

The root namespace in Cylc is a special one that all tasks inherit from.

(Edit: just noticed Hilary already mentioned it, but anyway there’s an explicit example)

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thanks a lot @hilary.j.oliver, now i understand the setup of the namespace syntax thing better and the example provided @MetRonnie works perfectly, brilliant!

i think what was confusing me was that the shorthand only had single [...] in it whereas what i needed was some [[...]]!

anyway, sorted now, much apprecaited.


Yeah, the problem is the number of brackets gets ridiculous for deep nesting.

Documented here: The .cylc File Format — Cylc 8.2.2 documentation

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