On Wed, Mar 01, 2023 at 01:39:52PM -0500, Theodore Ts'o wrote: > On Wed, Mar 01, 2023 at 06:17:59PM +0100, Michal Suchánek wrote: > > > Using a random number generator for clock can help, but it's only 13 > > > bits, so it's certainly not fool-proof. Given that using a time-based > > > UUID leaks the MAC address of your ethernet port as well as when the > > > UUID was generated (which can be interesting when you're curious say, > > > when a Libreoffice doc was created), in general best practice is to > > > use the random UUID type, especially given that modern Linux systems > > > all have the getrandom(2) system call. That gives you 58 bits of > > > entropy in the UUID, so that's probably the better way to go. > > > > That explains why I don't have a clock.txt file. I did not go out of my > > way to generate time-based uuids. > > Note that the only reason why you might be trying to generate a huge > number of time-based UUID is if you are running a database (cough, Thanks for the very detailed explanation. I suppose the default is fine for most users then, and makes it reasonably safe to use time basedd uuids for users of systems like Raspberry Pi which exhibit weird time jumps, likely due to lack of RTC battery. uuidd is provided for people who want to generate large quantities of UUIDs. When somebody *really* wants and it improves their use case they can mount tmpfs on /var/lib/libuuid/ Might be nice to write down in the uuid_generate man page if this is coming up repeatedly. Thanks Michal
