在具有测试通道的 FCOS 上, k3sup 不能正常工作

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I use k3sup to setup a k3s cluster on fcos nodes for personal cluster (libvirt vms). This used to work. Per this issue the stable channel doesn't have some rpms, but using the testing channel works. I verified that manually ssh'ing to the fcos node and running curl -sfL https://get.k3s.io | INSTALL_K3S_CHANNEL=testing sh - does work, as suggested in this comment. However, the equivalent version of this, to pass --k3s-channel testing to k3sup, does not work.