NCAS Computational Modelling Services

Cylc 8

Cylc 8 on PUMA2 and ARCHER2

Cylc 8 is available on PUMA2 and ARCHER2, but has not yet been widely used.
We are still testing the system, and so the software configuration is subject to change.

See the links below for further information. Report any issues to the helpdesk.


Cylc 8 replaces the Python 2 based Cylc 7 software. It is a complete rewrite in Python 3 and contains many changes from Cylc 7, so we encourage you to look at the documentation. The user interface system is still being developed and does not yet have full functionality.

Useful links:

Note that in Cylc 8 terminology “suites” have become “workflows”.

ARCHER2 workflows

Cylc-8 workflows available on ARCHER2:

Cylc 8 idCylc 7 idDescription
u-cc519/cylc8u-cc519N48 GA6 (training suite)

See the instructions for migrating an ARCHER2 Cylc 7 suite to Cylc 8.

Using Cylc 8 on PUMA2 and ARCHER2

Setting the Cylc version

Set the Cylc version in the terminal:


You should be able to do this alongside any Cylc 7 suites you have running.

Assuming you have set up your ARCHER2 and Jasmin environments to have Cylc 7 available, you should not need to make any further changes. The workflow will simply pick up the appropriate Cylc version when it runs.

Running a workflow

To run a simple test, copy the test.platforms.c8 workflow:

cd ~/roses
cp -r ~annette/roses/test.platforms.c8 . 

In the test.platforms.c8 directory, edit the rose-suite.conf file to set your ARCHER2 username and project code.

Run the workflow with:

cylc vip 

See the Cylc 8 cheat sheet for an overview of Cylc 8 commands.


The test.platforms.c8 workflow runs tasks on ARCHER2 and JASMIN in the background and via the Slurm scheduler.

Look in the cylc.flow file (this replaces suite.rc) to see how remote tasks are specified in Cylc 8. Tasks are assigned a “platform”, which combines the host and job running method. See the Cylc 8 platform documentation for details.

On PUMA2 the following platforms are available:

  • PUMA2:
    • localhost : background job
  • ARCHER2:
    • archer2 : Slurm job
    • archer2_bg : background on random login node
    • ln0[1-4]_bg : background job on specific login node
    • lotus : Slurm job
    • sci_bg : background job on random sci machine
    • sci[1-8]_bg : background job on specific sci machine

Note that multiplexing is no longer needed to submit jobs to Jasmin.

There are still sometimes issues if a host is not available, or not fully functional (for example if it can’t see the file system or Slurm queue).

Using the TUI

To track the progress of a running workflow via the terminal user interface:

cylc tui test.platforms.c8

You can’t do everything via this interface, so you still need to use the command line interface, for example to remove tasks from the graph or trigger tasks that are not visible in the current graph.

Using the web-based UI with port-forwarding

Copying the instructions documented here

First open an ssh tunnel, so that a given port on your local machine (e.g. your laptop) maps to the Cylc UI Server’s port on the HPC. On your local machine, type

$ ssh -N -L PORT:localhost:PORT HOST

where PORT is a valid port number and HOST is on the HPC. You will need to know the range of allowed ports (e.g.1024-49151). Choose any number in this range but make sure your port number is fairly unique to avoid clashing with other users. (Note the option -N opens the connection without logging you into the shell).

Then ssh to the host:

$ ssh HOST

and add the following to $HOME/.cylc/uiserver/ on the HOST.


where PORT and HOST match the values you selected when opening the ssh tunnel.

You’re now ready to fire up the web graphical interface

$ cylc gui

Just copy the URL that looks like

into your web browser. (Again substitute HOST and PORT with the values chosen above.)

Note that each user needs a unique port number.