[Florian Weimer] > That's not very different from /etc/machine-id, isn't it?
Ah, thank you very much for bringing this systemd setting to my attention. I was not aware of it. I agree that it seem very similar in purpose and implementation. Will it be available on non-linux Debian architectures too? >> We need to figure out how to transform the UUID to a 32 bit integer, >> of course. > > And I think this is the crux of the problem. Whatever we do, with > today's cluster sizes it's just not reliably unique. Well, for the set of machines we have available at work (ca. 3000) it would be sufficiently unique. For most sites it would make the return value from gethostid() unique. In most use cases it do not need need to globally unique. Like the ZFS use case, it just need to be unique among the hosts sharing the storage system. In another use case at work, it should be unique across the entire stock of linux machines. > You could use /etc/machine-id instead. Some effort goes into that to > make it actually unique. I will definitely put this systemd value in my tool box. Again, thank you very much for mentioning it. :) > DMI data seems risky because it depends on firmware, and there are so > many firmware bugs out there. I did not quite understand what you mean here. Do you mean the DMI value in your experience isn't unique? > It would also not address the matter of changing host IDs as the > result of host migrations. As far as I can tell, host migration could be solved by storing the wanted hostid in /etc/hostid when migrating. On an related note, I had a look at the POSIX definition for gethostuid()[1], and its "Upon successful completion, gethostid() shall return an identifier for the current host" is definitely very vague. So glibc is sure not violating POSIX by changing the value when the host changes IP address or commonly returning identical IDs on different machines, but real world applications on the other hand expect the hostid value to be reasonably unique and fixed across IP changes and reboots. [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/gethostid.html -- Happy hacking Petter Reinholdtsen