I searched my question and none of them answered me: Is machine-id as unique as mainboard UUID (fetched by "get csproduct UUID" command on windows)? And is enough reliable to bind a license on machine-id beside mac address? Or what is uuid on *nix system that can be used for licensing?

  • 1
    "machine-id" as found where, on what Linux?
    – Kusalananda
    Sep 30, 2017 at 16:12
  • On .../dbus/machine-id file. Sep 30, 2017 at 16:14

2 Answers 2


Yes, nowadays.

This is covered in the systemd manual. The value in /etc/machine-id was originally not a valid UUID, because the systemd people did not originally write correct code for generating a version 4 UUID. But this has since been fixed.

If you bind a licence to the machine ID, be aware that it can change …

  • … if someone deletes /etc/machine-id and it gets re-created at next bootstrap;
  • … if /etc (usually on the root volume in practice) is not mounted read-write at bootstrap, /etc/machine-id is invalid or missing, and /etc cannot be later re-mounted read-write allowing /etc/machine-id to be written;
  • … if the disc volume containing /etc is replaced with another, different, disc volume whilst the operating system is not running or someone changes the machine-id on the disc volume with a tool such as systemd-firstboot;
  • … if the system is what the systemd people call "stateless" and (effectively, it being slightly more complex than this) /etc/machine-id gets re-created at every bootstrap;
  • … inside containers on the machine.

But it, intentionally, does not change …

  • … if the mainboard, processor, or NIC is replaced;
  • … if the MAC addresses of NICs are changed;
  • … if the root volume (more specifically, the volume containing /etc) is imaged onto a replacement disc with something like dd or pax;
  • … during system runtime (unless the system administrator deliberately mucks around with it);
  • …from one bootstrap to the next if /etc/machine-id is valid, non-empty, and writable the first time around.

portability notes

  • Don't use /var/lib/dbus/machine-id in preference to /etc/machine-id.
    • The original Desktop Bus file which begat /etc/machine-id is unfortunately not in a fixed location that is portable across operating systems. On some systems one finds it at /var/lib/dbus/machine-id; on others at /var/db/dbus/machine-id.
    • Sometime around 2013, D-Bus was modified to make use of /etc/machine-id if it exists, superseding the file in /var, whereever it is.
    • In 2015, the Debian/Ubuntu people made the D-Bus file in /var default to being a symbolic link to /etc/machine-id, in any case.
  • /etc/machine-id is not limited to only being available in the bootstrap process after /var is mounted or after network interfaces are brought up.
  • Although vanilla FreeBSD/TrueOS, NetBSD, and OpenBSD do not provide a /etc/machine-id, the nosh toolset provides portable tools (that are also usable on Linux) for creating it that also know of the BSD-specific places that the BSDs expect such IDs and keep the twain consistent.

Further reading

  • The answer to "Is machine-id a uuid?" is as I wrote it.
    – JdeBP
    Oct 4, 2017 at 13:40
  • Then you were getting mixed up as to what answers what. (-:
    – JdeBP
    Oct 14, 2017 at 15:11
  • What do you mean by imaged onto a replacement disc with something like [...] pax? Are you talking of the POSIX pax (portable archiver) command? Mar 20, 2019 at 16:15
  • Something I ran into the other day: cloning a VM means the clone gets the same machine-id. And what makes matters worse, systemd uses it as the DHCP client identifier which means the clone will get the same IP address as the original. Mar 20, 2019 at 16:17
  • You should enjoy the DESCRIPTION and EXAMPLE USERS sections from the new machine-id manual page that I just put into the further reading. (-:
    – JdeBP
    Mar 21, 2019 at 0:58

From a quick Google search:

  • /etc/machine-id should be unique, and only change if the machine is reinstalled, but is provided by systemd, which many systems don't have
  • /var/lib/dbus/machine-id should be unique, and should be much more widely available. The docs say it can change if the hardware configuration changes, but in practice I think it only changes if the machine is reinstalled
  • you could use system-uuid, but you need to be root, and it will change if the motherboard changes

/var/lib/dbus/machine-id seems like the best method for most situations.

Further reading:

  • Which one of them may be useful for licensing? And how to get mainboard UUID on linux? Sep 30, 2017 at 16:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.