When the NUMA startup warning tries to determine if the host has more than 1 NUMA node, it looks for the existence of /sys/devices/system/node/node1. However, this is needlessly fragile because /sys might
- not be mounted,
- be mounted elsewhere,
- be missing certain hardware info (eg. NUMA nodes), or
- have restricted ownership or permissions (or be subject to other MAC restrictions like SELinux or AppArmor).
Better approaches to determine the number of NUMA nodes are to either use the get_mempolicy() Linux syscall, or as a fallback, look for a line starting with "Node 1" in /proc/zoneinfo.