UNIX-programming-timev
Photo by Takuya Oikawa on Flickr· CC BY-SA 2.0
Historically, UNIX systems have maintained two different time values:
Calendar time. This value counts the number of seconds since the Epoch: 00:00:00 January 1, 1970, Coordinated Universal Time (UTC). (Older manuals refer to UTC as Greenwich Mean Time.) These time values are used to record the time when a file was last modified, for example. The primitive system data type time_t holds these time values.
Process time. This is also called CPU time and measures the central processor resources used by a process. Process time is measured in clock ticks, which have historically been 50, 60, or 100 ticks per second. The primitive system data type clock_t holds these time values.
Shortly, time_t holds the calendar thing time and clock_t holds the process time values.
UNIX systems maintains three values for a process :
Clock time
User CPU time
System CPU time
-The clock time, is the amount of time the process takes to ru9n, and its value depends on the number of other processes being run on the system. The time between the start and the end of a process.
-User CPU time is the the time which is cpu waste for you like usermode process (for example mathematical processes)
-Sytem CPU time is the the time which is cpu waste for kernel mode processes like (file read and write, syscalls and smth else.)
Its the shi
The output format from the time command depends on the shell being used, because some shells don't run /usr/bin/time , but instead have a separate built-in function to measure the time it takes commands to run.
