After more tests, the situation clears a bit.If "COREs=0,1" (etc) is present in the `gres.conf` file, then one can inject gres jobs on a single core only by using `--gres-flags=disable-bindung` if a non-gres job is running the same node.
If "COREs=0,1" is NOT present in `gres.conf`. then any gres job can enter the node irrespective of the `--gres-flags`. At least this is what I observe on my simulated slurm 18.08.5 cluster.
The above mentioned behavior complies with the manpages of slurm. That is good.
The behavior is different on our real machine. I'll try to dig down why. But for now, we can consider this thread closed. Thanks to everyone for your help.
smime.p7s
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