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

Question

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

I only know, I can call "ps -p my_process_id -f" and then parse the output. But it is not cool.

Answer 1

If you are doing it from within the python program you're trying to measure, you could do something like this:

import time
# at the beginning of the script
startTime = time.time()
# ...
def getUptime():
    """
    Returns the number of seconds since the program started.
    """
    # do return startTime if you just want the process start time
    return time.time() - startTime

Otherwise, you have no choice but to parse ps or go into /proc/pid. A nice bashy way of getting the elapsed time is:

ps -eo pid,etime | grep $YOUR_PID | awk '{print $2}'

This will only print the elapsed time in the following format, so it should be quite easy to parse:

days-HH:MM:SS

(if it's been running for less than a day, it's just HH:MM:SS)

The start time is available like this:

ps -eo pid,stime | grep $YOUR_PID | awk '{print $2}'

Unfortunately, if your process didn't start today, this will only give you the date that it started, rather than the time.

The best way of doing this is to get the elapsed time and the current time and just do a bit of math. The following is a python script that takes a PID as an argument and does the above for you, printing out the start date and time of the process:

import sys
import datetime
import time
import subprocess

# call like this: python startTime.py $PID

pid = sys.argv[1]
proc = subprocess.Popen(['ps','-eo','pid,etime'], stdout=subprocess.PIPE)
# get data from stdout
proc.wait()
results = proc.stdout.readlines()
# parse data (should only be one)
for result in results:
    try:
        result.strip()
        if result.split()[0] == pid:
            pidInfo = result.split()[1]
            # stop after the first one we find
            break
    except IndexError:
        pass # ignore it
else:
    # didn't find one
    print "Process PID", pid, "doesn't seem to exist!"
    sys.exit(0)
pidInfo = [result.split()[1] for result in results
           if result.split()[0] == pid][0]
pidInfo = pidInfo.partition("-")
if pidInfo[1] == '-':
    # there is a day
    days = int(pidInfo[0])
    rest = pidInfo[2].split(":")
    hours = int(rest[0])
    minutes = int(rest[1])
    seconds = int(rest[2])
else:
    days = 0
    rest = pidInfo[0].split(":")
    if len(rest) == 3:
        hours = int(rest[0])
        minutes = int(rest[1])
        seconds = int(rest[2])
    elif len(rest) == 2:
        hours = 0
        minutes = int(rest[0])
        seconds = int(rest[1])
    else:
        hours = 0
        minutes = 0
        seconds = int(rest[0])

# get the start time
secondsSinceStart = days*24*3600 + hours*3600 + minutes*60 + seconds
# unix time (in seconds) of start
startTime = time.time() - secondsSinceStart
# final result
print "Process started on",
print datetime.datetime.fromtimestamp(startTime).strftime("%a %b %d at %I:%M:%S %p")