Measuring Program Resource Use

The GNU time Command

Edition 1.7, for version 1.7

8 February 2000

Table of Contents

• Measuring Program Resource Use
  • Setting the Output Format
  • The Format String
    • Time Resources
    • Memory Resources
    • I/O Resources
    • Command Info
  • Redirecting Output
  • Examples
  • Accuracy
  • Running the time Command

Measuring Program Resource Use

The time command runs another program, then displays information about the resources used by that program, collected by the system while the program was running. You can select which information is reported and the format in which it is shown (see section Setting the Output Format), or have time save the information in a file instead of displaying it on the screen (see section Redirecting Output).

The resources that time can report on fall into the general categories of time, memory, and I/O and IPC calls. Some systems do not provide much information about program resource use; time reports unavailable information as zero values (see section Accuracy).

The format of the time command is:

time [option...] command [arg...]

time runs the program command, with any given arguments arg.... When command finishes, time displays information about resources used by command.

Here is an example of using time to measure the time and other resources used by running the program grep:

eg$ time grep nobody /etc/aliases
nobody:/dev/null
etc-files:nobody
misc-group:nobody
0.07user 0.50system 0:06.69elapsed 8%CPU (0avgtext+489avgdata 324maxresident)k
46inputs+7outputs (43major+251minor)pagefaults 0swaps

Mail suggestions and bug reports for GNU time to bug-gnu-utils@prep.ai.mit.edu. Please include the version of time, which you can get by running `time --version', and the operating system and C compiler you used.

Setting the Output Format

time uses a format string to determine which information to display about the resources used by the command it runs. See section The Format String, for the interpretation of the format string contents.

You can specify a format string with the command line options listed below. If no format is specified on the command line, but the TIME environment variable is set, its value is used as the format string. Otherwise, the default format built into time is used:

%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
%Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps

The command line options to set the format are:

-f format

--format=format

Use format as the format string.

-p