Question

What is the best-practiced way to get an unique machine ID in GNU/Linux for i386 architecture?

Are there any good ways except the mac address?

Answer 1

Depending on your kernel, the DMI information may be available via sysfs.
Try those:

# cat /sys/class/dmi/id/board_serial
xxxxxxxxxxxxxxx
# cat /sys/class/dmi/id/product_uuid
xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

or using a tool

# dmidecode -s baseboard-serial-number
...
# dmidecode -s system-uuid
...