How to retrieve the process start time (or uptime) in python

By using psutil https://github.com/giampaolo/psutil:

>>> import psutil, os, time
>>> p = psutil.Process(os.getpid())
>>> p.create_time()
1293678383.0799999
>>> time.strftime("%Y-%m-%d %H:%M:%S", time.localtime(p.create_time()))
'2010-12-30 04:06:23'
>>>

…plus it’s cross platform, not only Linux.

NB: I am one of the authors of this project.