Mastering Linux /usr/bin/time: Options, Formats, and Resource Metrics

When you need to analyze a program’s performance on Linux—such as user‑mode time, kernel‑mode time, average memory usage, and other metrics—the dedicated /usr/bin/time utility provides detailed resource information.

The basic syntax is: /usr/bin/time [options] program [arguments] Options are optional flags or values that modify the output. Common options include: -v or --verbose: produce a detailed description. --quiet: suppress status messages. -f or --format: specify a custom output format. -p or --portability: use POSIX‑compatible output. -o FILE or --output=FILE: redirect output to a file (overwrites). -a or --append: append output to the file instead of overwriting.

Running time without options yields a default output similar to:

real %e
user %U
sys %S

Custom formats are defined with a format string containing resource specifiers prefixed by %. Escape sequences such as \t (tab) and \n (newline) are supported. Example:

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

This prints user time, system time, and exit status in a tab‑separated line.

Resource Specifiers

The utility can report a wide range of metrics, each identified by a single‑letter specifier (from the manual page). Notable ones include:

C : command name and arguments.

D : average size of the non‑shared data segment (KB).

E : elapsed real (wall‑clock) time ([hh:]mm:ss).

F : major page faults (I/O‑required).

I : file system inputs.

K : average total memory (data+stack+text) in KB.

M : maximum resident set size (KB).

O : file system outputs.

P : CPU usage percentage (user+system / elapsed).

R : minor (recoverable) page faults.

S : CPU seconds spent in kernel mode.

U : CPU seconds spent in user mode.

W : number of swaps.

X : average shared text size (KB).

Z : system page size (bytes).

c : involuntary context switches.

e : elapsed real time in seconds.

k : signals delivered to the process.

p : average non‑shared stack size (KB).

r : sockets messages received.

s : sockets messages sent.

t : average resident set size (KB).

w : voluntary context switches.

x : exit status of the command.

These specifiers allow you to tailor the output to the exact metrics you need for performance analysis.

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

The shell’s built‑in time command differs from /usr/bin/time. Invoking time without the full path may call the built‑in, which lacks many options and may produce different formatting. To access the full feature set, use the explicit path or ensure the external binary precedes the built‑in in your PATH.

For detailed information, consult the manual page with man time for the external utility, or use help time for the built‑in version.