Master Linux Resource Monitoring with /usr/bin/time: Options, Formats, and Tips

When you need to analyze a program’s resource consumption—such as user‑mode time, kernel‑mode time, average memory usage, or other metrics—Linux provides a dedicated utility called /usr/bin/time. It takes a program name (and optional arguments) and reports detailed resource information, also warning you if the command exits with a non‑zero status.

Basic Syntax

The general form is: /usr/bin/time [options] program [arguments] "Options" are optional flags that enable or disable specific features of the utility.

Common Options

-v

, --verbose: Output a detailed description of resource usage. --quiet: Suppress status messages from the time utility. -f, --format: Allow the user to control the output format with a custom format string. -p, --portability: Produce output that conforms to the POSIX standard. -o FILE, --output=FILE: Redirect the utility’s output to FILE, overwriting it. -a, --append: Append the output to FILE instead of overwriting.

Default Output Example

Running /usr/bin/time ls without options yields output similar to:

# /usr/bin/time ls
0.00user 0.00system 0.00:00.00elapsed 0%CPU (0avgtext+0avgdata 3888maxresident)k
0inputs+0outputs (0major+304minor)pagefaults 0swaps

The last two lines contain the resource‑usage information.

Custom Format Strings

Using -f you can specify a format string composed of “resource specifiers” prefixed by %. Escape sequences such as \t (tab) and \n (newline) are supported. Text not part of a specifier is copied verbatim.

Example:

/usr/bin/time -f "\t%U user,\t%S system,\t%x status" date

Produces output like:

0.00 user,    0.00 system,    0 status

Resource Specifiers

Below is a non‑exhaustive list of specifiers available in the manual page: C: Command name and arguments. D: Average size of the process’s non‑shared data segment (KB). E: Elapsed real (wall‑clock) time, [hours:]minutes:seconds. F: Number of major (I/O‑requiring) page faults. I: Number of file system inputs. K: Average total (data+stack+text) memory usage (KB). M: Maximum resident set size (KB). O: Number of file system outputs. P: Percentage of CPU used (user+system)/elapsed. R: Number of minor (recoverable) page faults. S: CPU seconds spent in kernel mode. U: CPU seconds spent in user mode. W: Number of times the process was swapped out. X: Average amount of shared text (KB). Z: System page size (bytes). c: Number of involuntary context switches. e: Elapsed real time (seconds). k: Number of signals delivered to the process. p: Average non‑shared stack size (KB). r: Number of socket messages received. s: Number of socket messages sent. t: Average resident set size (KB). w: Number of voluntary context switches. x: Exit status of the command.

Why Use /usr/bin/time Instead of the Shell Built‑in?

The shell’s built‑in time command lacks many of the formatting options provided by the external utility. Invoking time without the full path runs the built‑in, which may reject flags like -f and produce unexpected output. To access the full feature set, always call the external binary with its absolute path, e.g., /usr/bin/time. You can consult its manual with man time and view the built‑in’s help with help time.