I'm looking for a fast and lightweight way to read system uptime from a Python script. Is there a way to call the sysinfo Linux system call from Python?
So far I've found two other methods for measuring uptime, one that involves running an external processes and one that involves reading a file in /proc.
import subprocess
def uptime1():
raw = subprocess.check_output('uptime').decode("utf8").replace(',', '')
days = int(raw.split()[2])
if 'min' in raw:
hours = 0
minutes = int(raw[4])
else:
hours, minutes = map(int,raw.split()[4].split(':'))
totalsecs = ((days * 24 + hours) * 60 + minutes) * 60
return totalsecs
def uptime2():
with open('/proc/uptime', 'r') as f:
uptime_seconds = float(f.readline().split()[0])
return uptime_seconds
When comparing the speed, the second method is around 50 times faster. Still, calling a system call directly should be yet another order of magnitude better.
>> import timeit
>> print(timeit.timeit('ut.uptime1()', setup="import uptimecalls as ut", number=1000))
1.7286969429987948
>> print(timeit.timeit('ut.uptime2()', setup="import uptimecalls as ut", number=1000))
0.03355383600865025
You can try installing psutil with:
pip install psutil
and then use the following fragment of code:
import psutil
import time
def seconds_elapsed():
return time.time() - psutil.boot_time()
print seconds_elapsed()
I don't think you can get much faster than using ctypes to call sysinfo() but in my tests, its slower than /proc. Those linux system programmers seem to know what they are doing!
import ctypes
import struct
def uptime3():
libc = ctypes.CDLL('libc.so.6')
buf = ctypes.create_string_buffer(4096) # generous buffer to hold
# struct sysinfo
if libc.sysinfo(buf) != 0:
print('failed')
return -1
uptime = struct.unpack_from('@l', buf.raw)[0]
return uptime
Running your two tests plus mine on my slow laptop, I got:
>>> print(timeit.timeit('ut.uptime1()', setup="import uptimecalls as ut", number=1000))
5.284219555993332
>>> print(timeit.timeit('ut.uptime2()', setup="import uptimecalls as ut", number=1000))
0.1044210599939106
>>> print(timeit.timeit('ut.uptime3()', setup="import uptimecalls as ut", number=1000))
0.11733305400412064
UPDATE
Most of the time is spent pulling in libc and creating the buffer. If you plan to make the call repeatedly over time, then you can pull those steps out of the function and measure just the system call. In that case, this solution is the clear winner:
uptime1: 5.066633300986723
uptime2: 0.11561189399799332
uptime3: 0.007740753993857652