Master Linux Resource Monitoring: How to Use /usr/bin/time Effectively

Overview

Sometimes you may want to analyze your program based on parameters such as time spent in user mode, time spent in kernel mode, average memory usage, etc. Linux provides a dedicated utility called time for this purpose.

Syntax

/usr/bin/time [options] program [arguments]

Common Options

-v, --verbose

: output a detailed description. --quiet: suppress status messages. -f, --format: control output format. -p, --portability: produce POSIX‑compatible output. -o FILE, --output=FILE: redirect output to a file (overwrites). -a, --append: append output to a file instead of overwriting.

Sample Output

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

Format Options

Custom format strings consist of resource specifiers introduced by %. Escape sequences such as \t (tab) and \n (newline) are supported. Text not part of a specifier is copied verbatim.

$ /usr/bin/time -f "\t%U user,\t%S system,\t%x status" date
Sun Jan 22 17:46:58 IST 2012
0.00 user, 0.00 system, 0 status

Resource Specifiers

Below is a non‑exhaustive list of specifiers that time can report (excerpt from the manual page): C: command name and arguments. D: average size of the unshared data segment (KB). E: elapsed real (wall‑clock) time ([hh:]mm:ss). F: major page faults. I: number of file system inputs. K: average total memory usage (KB). M: maximum resident set size (KB). O: number of file system outputs. P: CPU percentage (user+system)/elapsed. R: minor (reclaimable) page faults. S: CPU seconds spent in kernel mode. U: CPU seconds spent in user mode. W: number of swaps. X: average size of shared text (KB). Z: system page size (bytes). c: involuntary context switches. e: elapsed real time (seconds). k: number of signals delivered. p: average unshared stack size (KB). r: number of socket messages received. s: number of socket messages sent. t: average resident set size (KB). w: voluntary context switches. x: exit status.

Why Use /usr/bin/time?

The shell built‑in time does not accept the same options as the external /usr/bin/time. Invoking time without the full path may result in errors such as “command not found” for -f. To access the full feature set, call the external binary explicitly.

Use man time to view the manual for /usr/bin/time and help time for the built‑in version.