Snowflake: Simple Persistent System-wide Unique IDs
I've often found myself needing to have a per-machine unique identifier, but actually getting one of these is harder than it should be. You can't just use the MAC address, since those aren't guaranteed to be unique, especially when you're working with a batch of cheap embedded devices. While not rocket science, it's also not trivial to get the MAC address of a box sometimes: which interface to use? What if you change network cards? What if you have to spoof a MAC address? POSIX specifies gethostid(1), but on Linux the man page notes under "Bugs" that "It is impossible to ensure that the identifier is globally unique." Indeed, my laptop and my work computer have the same hostid value.
Snowflake is a trivial wrapper around Python's uuid library to create a persistent, per-machine UUID (called a 'snowflake') and give you a nice API to mess with it. Usage is simple:
>>> import snowflake >>> snowflake.snowflake() '7232c1c3-f6d1-4aec-bedd-c7e4c10dc8d3'
There's also a script that can be run from the command line:
$ snowflake 7232c1c3-f6d1-4aec-bedd-c7e4c10dc8d3
Installation and Setup
To generate a machine's snowflake ID, just install snowflake:
$ pip install snowflake
Or from source:
$ python setup.py install
The machine's snowflake is saved in /etc/snowflake during installation. Any user can read this file, but only users with root access can modify it. You can also generate other snowflakes in other locations, so each user (or application) can make their own snowflakes.
Of course, you can do all this in Python too:
>>> import snowflake >>> snowflake.make_snowflake(snowflake_file='foo') ee2b1891-ccd3-4a23-9246-4ce40d20e740 >>> snowflake.snowflake(snowflake_file='foo') ee2b1891-ccd3-4a23-9246-4ce40d20e740
Right now, snowflake only works on Unix-y systems.
Copyright (c) 2012, Shaddi Hasan All rights reserved.
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