times

What times Does

The times command displays the cumulative CPU time used by the current shell process and all its child processes. This time is broken down into two categories:

• User time: The time spent executing the process’s own code.
• System time: The time spent executing kernel code on behalf of the process.

This breakdown is provided separately for both the current shell and its children. Understanding this helps in diagnosing whether a process is CPU-bound (high user time) or I/O-bound (high system time).

Syntax and Options

The basic syntax is incredibly simple:

times

Executing this command will output a line similar to this (the exact numbers will vary):

0m0.000s 0m0.005s 0m0.000s 0m0.005s

This represents (in order):

• User time for the shell
• System time for the shell
• User time for child processes
• System time for child processes

While the basic usage is straightforward, there are no additional options available for the times command itself. Its simplicity is its strength.

Example Usage Scenarios

Let’s illustrate times with some examples:

Example 1: Measuring a simple command:

First, let’s record the baseline CPU time:

times

Now, let’s run a computationally intensive command (like a long sleep):

sleep 5

Finally, check the CPU time again:

times

By subtracting the first times output from the second, you can estimate the CPU time consumed by the sleep command.

Example 2: Observing Child Process Behavior:

Run a command that spawns multiple child processes (e.g., a loop that calls sleep multiple times), execute times before and after to observe the effect on child process time. The difference in child process times will reflect the combined CPU usage of those spawned processes.

times
for i in {1..5}; do sleep 1 & done; wait
times

This script runs five sleep 1 commands concurrently in the background and waits for them to finish. Comparing the times outputs before and after this loop shows the additional user and system time consumed by the child processes.

Example 3: Identifying Potential Bottlenecks:

If a specific program or shell script is running slowly, use times before and after its execution to pinpoint whether the performance issue stems from extensive user computation or frequent system calls. A disproportionately high system time might indicate I/O bottlenecks, while a high user time could suggest optimization needs within the program’s code itself.

This capability makes times a simple yet effective tool for basic performance analysis directly within your shell environment. It’s an addition to your Linux command-line toolbox.