I prepared a qemu-x86-64 disk image that can reproduce this symptom at https://drive.google.com/drive/folders/1ObSUu3DCF2r4tzcGrykhBCRpPSemHNiu
After logging in as root with password root, systemd-nspawn -M container1 -n -b reproduces the symptom, that is, /bin/systemd-sysusers talks with rpcbind.socket before rpcbind.service is started, and hangs up. Ryutaroh
