When the startup is hung, do Code: grep copy_net_ns /proc/*/stack If that returns anything, you're having this issue. I can confirm that the issue is still present (but less frequent) on recent 4.15.x Proxmox PVE kernels. The Ubuntu kernel team acknowledged this bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1779678 The only solution provided was to use kernel 4.18. I was able to build and boot 4.18 with Proxmox but it breaks the current version of AppArmor with multiple "Profile doesn't conform to protocol" errors. The solution is build a new AppArmor but I haven't gotten that far yet.