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System time

Posted on 2003-11-20
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Last Modified: 2010-04-22
How can i retrieve the system time that is elapsed since Linux was started?

Thanks!!
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Question by:linux_newb
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9 Comments
 
LVL 45

Expert Comment

by:sunnycoder
ID: 9794242
uptime
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by:linux_newb
ID: 9794626
uptime is a shell command . I want to use this value in my prog. Isn't there any function which can be used to assign this value to a variable inside my program?
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by:sunnycoder
sunnycoder earned 20 total points
ID: 9794655
you can invoke it using popen() and read in the string into a char array
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LVL 3

Accepted Solution

by:
scn earned 20 total points
ID: 9795523
man 2 times
times( ) returns the number of jiffies elapsed since system was started.
Seconds = jiffies / HZ  (HZ is defined in include "asm/param.h")
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Expert Comment

by:S_KuMaaaaR
ID: 9817212
var=`uptime`

where var is ur program variable.

sanjeev
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Author Comment

by:linux_newb
ID: 9830512
> you can invoke it using popen() and read in the string into a char array

i hope the format of info by uptime remains same for all versions of  redHat... else it would be difficult to extract the reqd part  from the string.
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Expert Comment

by:sunnycoder
ID: 9830559
>i hope the format of info by uptime remains same for all versions of  redHat
for redhat it should be the same (cant say definitely about <6) ... any case I feel that scn's method is far superior in terms of portability and ease

from the times man page

The function times returns the number of clock ticks that have elapsed since an arbitrary point in the past. For Linux this point is the moment the system was booted. This return value may overflow the possible range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appropriately.

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Author Comment

by:linux_newb
ID: 9830564
i meant i am relying on the fact that elapsed time immediately follows word 'up'
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Expert Comment

by:sunnycoder
ID: 9830569
>i meant i am relying on the fact that elapsed time immediately follows word 'up'
should work .... if you are concerned then it can also be obtained from the proc filesystem ...
cat /proc/uptime
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