The good news is that most problems can easily be repaired with just a few steps. There are other steps you can take if none of the options on this list corrected the problem, but be warned: they are far more intensive and require quite a bit of knowledge about computers. If you aren’t comfortable taking steps like this, consider allowing a professional to make the repairs.Timing a Linux program helps one to understand how much time was spent. The versatile Linux time command can be used for this. User time is the time the program runs in user-mode, or in other words, outside of the kernel. The sys time is the time the program runs inside the kernel. It is important to note that both user time and sys time are actual CPU time spent inside user-mode and inside the kernel, respectively. In other words, when a program is blocked for a while and is not using the CPU, such time will not count towards user or sys times. Knowing this, we can accurately measure how much effective CPU time was used (by combining them). An example can be seen when timing sleep: time sleep 1 Given that user and sys times report CPU time only, whereas real time reports actual wall clock time, it is (thus) very common to see the time tool return output where a combination of user + sys does not equal real time. Here we timed the sleep command using the time tool. As we can see, our real time (1.001 seconds) matches our wall clock time, and requested time ( sleep 1 requests a sleep of one second) very well. We also see that extremely little CPU time had to be spent on the command as a whole: combining user + sys time, we see that only 0.001 seconds were spent. However, as the time manual states: “When the running time of a command is very nearly zero, some values (e.g., the percentage of CPU used) may be reported as either zero (which is wrong) or a question mark.” Using time For Performance Measuring We can also, likely incorrectly, deduce that the kernel was not involved in this command, as the sys time is effectively 0. We can use time to evaluate how long given actions will take (i.e., wall clock time) and how much CPU time they consumed while doing so. As a simple example, we could evaluate if any file system cache is operating on our system. To do so, we could jump into the /usr directory, which could easily hold 200k to 500k files on a commonplace Linux installation. Then, an alternative command can be used. That alternative command (or solution/implementation – i.e., multiple commands taken together as a single piece of code to be timed) can then be timed again.
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