Linux_host desktop fails with "no implicit conversion of nil into String"

Hi folks, just getting started on Alma 8 with rpm-based OnDemand v. 2.0.23. I have a trivial linux_host cluster set up; file browser and ssh/shell access are working fine. When I try to start a desktop session, I’m getting the above error. Without more information (file? line number? stack trace?), I’m not sure where to go next. I’m not doing any containerizing, for the moment just trying to get a browser-based Linux desktop working on the host OS. Nothing useful in any of the logs I’ve seen. Any helpful debugging next steps are most appreciated. Thanks!

Relevant files follow…

cat /etc/ood/config/clusters.d/davidtest.yml

title: “davidtest”
host: “”
adapter: “linux_host”
submit_host: “”
ssh_hosts: # These are the actual login nodes
site_timeout: 7200
debug: true
tmux_bin: /usr/bin/tmux

cat /etc/ood/config/apps/bc_desktop/davidtest.yml

title: “Davidtest Desktop”
description: “XFCE desktop on davidtest”
cluster: “davidtest”
desktop: “xfce”

Hi and welcome!

You may have a log entry in /var/log/ondemand-nginx/$USER/error.log.

But you’re right, without it it’s hard to saw where it’s coming from without that. I can’t exactly tell if your YAML correctly formatted, but I’d guess it is and it looks to be complete. Let’s hope there’s a message for us in that log.

Hey Jeff, yeah, checked that, unfortunately, nothing more what displays on the browser:

App 21942 output: [2022-06-10 14:49:28 -0500 ] INFO “execve = [“git”, “describe”, “–always”, “–tags”]”
App 21942 output: [2022-06-10 14:49:28 -0500 ] INFO “method=GET path=/pun/sys/dashboard/batch_connect/sys/bc_desktop/davidtest/session_contexts/new format=html controller=BatchConnect::SessionContextsController action=new status=200 duration=24.09 view=14.63”
App 21942 output: [2022-06-10 14:49:38 -0500 ] ERROR “ERROR: TypeError - no implicit conversion of nil into String”
App 21942 output: [2022-06-10 14:49:38 -0500 ] INFO “execve = [“git”, “describe”, “–always”, “–tags”]”
App 21942 output: [2022-06-10 14:49:38 -0500 ] INFO “method=POST path=/pun/sys/dashboard/batch_connect/sys/bc_desktop/davidtest/session_contexts format=html controller=BatchConnect::SessionContextsController action=create status=200 duration=91.94 view=15.03”

Can you share the app’s form YAML? I’m guessing some misconfiguration/something about that file is throwing this off.

i’m having a similar problem. is there a way to increase the logging or get a stack trace of the error in the logs?

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in case someone else hits this:

I encountered the same error message, it’s indeed hard to debug, but in my case it was because singularity_image was not defined in the yaml file, adding it solved that particular problem

I then encountered a value must be enumerable error, and that in turn was because my yaml syntax for ssh_hosts was wrong

after that linux_host is working like a charm, and it can be quite useful!

so, it would be good if the logs could point more closely to where the error is coming from, but I guess at least in my case there’s no substitute for reading the documentation (it does say that singularity_image needs to be defined) and for being careful when writing yaml files :sweat_smile: