When multiple hosts running systemd share the same NFS root, they will also share the same machine-id. This can cause issues, especially with journald. Journald logging can be disabled by deleting /var/log/journal which solves most of the problems, but a better solution is to use unique machine-id values on all of the hosts. Modern motherboards provide a unique UUID accessible via DMI, so a reasonable option is to write this out to /run during boot and point systemd at that as the machine-id. Here is a simple way to set that up.
Create the file /etc/initramfs-tools/scripts/init-top/machineid:
#!/bin/sh -e PREREQS="" prereqs() { echo "$PREREQS"; } case "$1" in prereqs) prereqs exit 0 ;; esac # write sanitized motherboard UUID to /run/machine-id sed 's/-//g' /sys/class/dmi/id/product_uuid > /run/machine-id # requires the following symbolic links: # ln -sf /run/machine-id /etc/machine-id # ln -sf /run/machine-id /var/lib/dbus/machine-id
Rebuild the initramfs (for example update-initramfs -u) and replace /etc/machine-id and /var/lib/dbus/machine-id with symlinks to /run/machine-id.