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File: time.info,  Node: Top,  Next: Resource Measurement,  Up: (dir)

The GNU 'time' Command
**********************

This file documents the the GNU 'time' command for running programs and
summarizing the system resources they use.  This is edition 1.7, for
version 1.7.

* Menu:

* Resource Measurement::  Measuring program resource use.
* Concept index::  Index of concepts.

File: time.info,  Node: Resource Measurement,  Next: Concept index,  Prev: Top,  Up: Top

1 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 (*note Setting Format::), or have 'time'
save the information in a file instead of displaying it on the screen
(*note Redirecting::).

   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 (*note 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 AT gnu.org'.  Please include the version of 'time', which
you can get by running 'time --version', and the operating system and C
compiler you used.

* Menu:

* Setting Format::      Selecting the information reported by 'time'.
* Format String::	The information 'time' can report.
* Redirecting::         Writing the information to a file.
* Examples::		Examples of using 'time'.
* Accuracy::		Limitations on the accuracy of 'time' output.
* Invoking time::	Summary of the options to the 'time' command.

File: time.info,  Node: Setting Format,  Next: Format String,  Up: Resource Measurement

1.1 Setting the Output Format
=============================

'time' uses a "format string" to determine which information to display
about the resources used by the command it runs.  *Note 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'
'--portability'
     Use the following format string:

          real %e
          user %U
          sys %S

     The default output format of time differs widely between
     implementations.  This option (in its short form -p) is supported
     by all POSIX-compliant 'time' implementations to retrieve basic
     information in the described format.

'-q'
'--quiet'
     Suppress non-zero error code from the executed program.

'-v'
'--verbose'
     Use the built-in verbose format, which displays each available
     piece of information on the program's resource use on its own line,
     with an English description of its meaning.

File: time.info,  Node: Format String,  Next: Redirecting,  Prev: Setting Format,  Up: Resource Measurement

1.2 The Format String
=====================

The "format string" controls the contents of the 'time' output.  It
consists of "resource specifiers" and "escapes", interspersed with plain
text.

   A backslash introduces an "escape", which is translated into a single
printing character upon output.  The valid escapes are listed below.  An
invalid escape is output as a question mark followed by a backslash.

'\t'
     a tab character

'\n'
     a newline

'\\'
     a literal backslash

   'time' always prints a newline after printing the resource use
information, so normally format strings do not end with a newline
character (or '\n').

   A resource specifier consists of a percent sign followed by another
character.  An invalid resource specifier is output as a question mark
followed by the invalid character.  Use '%%' to output a literal percent
sign.

   The resource specifiers, which are a superset of those recognized by
the 'tcsh' builtin 'time' command, are listed below.  Not all resources
are measured by all versions of Unix, so some of the values might be
reported as zero (*note Accuracy::).

* Menu:

* Time Resources::
* Memory Resources::
* I/O Resources::
* Command Info::

File: time.info,  Node: Time Resources,  Next: Memory Resources,  Up: Format String

1.2.1 Time Resources
--------------------

'E'
     Elapsed real (wall clock) time used by the process, in
     [hours:]minutes:seconds.

'e'
     Elapsed real (wall clock) time used by the process, in seconds.

'S'
     Total number of CPU-seconds used by the system on behalf of the
     process (in kernel mode), in seconds.

'U'
     Total number of CPU-seconds that the process used directly (in user
     mode), in seconds.

'P'
     Percentage of the CPU that this job got.  This is just user +
     system times divied by the total running time.

File: time.info,  Node: Memory Resources,  Next: I/O Resources,  Prev: Time Resources,  Up: Format String

1.2.2 Memory Resources
----------------------

'M'
     Maximum resident set size of the process during its lifetime, in
     Kilobytes.

't'
     Average resident set size of the process, in Kilobytes.

'K'
     Average total (data+stack+text) memory use of the process, in
     Kilobytes.

'D'
     Average size of the process's unshared data area, in Kilobytes.

'p'
     Average size of the process's unshared stack, in Kilobytes.

'X'
     Average size of the process's shared text, in Kilobytes.

'Z'
     System's page size, in bytes.  This is a per-system constant, but
     varies between systems.

File: time.info,  Node: I/O Resources,  Next: Command Info,  Prev: Memory Resources,  Up: Format String

1.2.3 I/O Resources
-------------------

'F'
     Number of major, or I/O-requiring, page faults that occurred while
     the process was running.  These are faults where the page has
     actually migrated out of primary memory.

'R'
     Number of minor, or recoverable, page faults.  These are pages that
     are not valid (so they fault) but which have not yet been claimed
     by other virtual pages.  Thus the data in the page is still valid
     but the system tables must be updated.

'W'
     Number of times the process was swapped out of main memory.

'c'
     Number of times the process was context-switched involuntarily
     (because the time slice expired).

'w'
     Number of times that the program was context-switched voluntarily,
     for instance while waiting for an I/O operation to complete.

'I'
     Number of file system inputs by the process.

'O'
     Number of file system outputs by the process.

'r'
     Number of socket messages received by the process.

's'
     Number of socket messages sent by the process.

'k'
     Number of signals delivered to the process.

File: time.info,  Node: Command Info,  Prev: I/O Resources,  Up: Format String

1.2.4 Command Info
------------------

'C'
     Name and command line arguments of the command being timed.

'x'
     Exit status of the command.

File: time.info,  Node: Redirecting,  Next: Examples,  Prev: Format String,  Up: Resource Measurement

1.3 Redirecting Output
======================

By default, 'time' writes the resource use statistics to the standard
error stream.  The options below make it write the statistics to a file
instead.  Doing this can be useful if the program you're running writes
to the standard error or you're running 'time' noninteractively or in
the background.

'-o FILE'
'--output=FILE'
     Write the resource use statistics to FILE.  By default, this
     _overwrites_ the file, destroying the file's previous contents.

'-a'
'--append'
     _Append_ the resource use information to the output file instead of
     overwriting it.  This option is only useful with the '-o' or
     '--output' option.

File: time.info,  Node: Examples,  Next: Accuracy,  Prev: Redirecting,  Up: Resource Measurement

1.4 Examples
============

Run the command 'wc /etc/hosts' and show the default information:

     eg$ time wc /etc/hosts
           35     111    1134 /etc/hosts
     0.00user 0.01system 0:00.04elapsed 25%CPU (0avgtext+0avgdata 0maxresident)k
     1inputs+1outputs (0major+0minor)pagefaults 0swaps

Run the command 'ls -Fs' and show just the user, system, and wall-clock
time:

     eg$ time -f "\t%E real,\t%U user,\t%S sys" ls -Fs
     total 16
     1 account/      1 db/           1 mail/         1 run/
     1 backups/      1 emacs/        1 msgs/         1 rwho/
     1 crash/        1 games/        1 preserve/     1 spool/
     1 cron/         1 log/          1 quotas/       1 tmp/
             0:00.03 real,   0.00 user,      0.01 sys

Edit the file '.bashrc' and have 'time' append the elapsed time and
number of signals to the file 'log', reading the format string from the
environment variable 'TIME':

     eg$ export TIME="\t%E,\t%k" # If using bash or ksh
     eg$ setenv TIME "\t%E,\t%k" # If using csh or tcsh
     eg$ time -a -o log emacs .bashrc
     eg$ cat log
             0:16.55,        726

Run the command 'sleep 4' and show all of the information about it
verbosely:

     eg$ time -v sleep 4
             Command being timed: "sleep 4"
             User time (seconds): 0.00
             System time (seconds): 0.05
             Percent of CPU this job got: 1%
             Elapsed (wall clock) time (h:mm:ss or m:ss): 0:04.26
             Average shared text size (kbytes): 36
             Average unshared data size (kbytes): 24
             Average stack size (kbytes): 0
             Average total size (kbytes): 60
             Maximum resident set size (kbytes): 32
             Average resident set size (kbytes): 24
             Major (requiring I/O) page faults: 3
             Minor (reclaiming a frame) page faults: 0
             Voluntary context switches: 11
             Involuntary context switches: 0
             Swaps: 0
             File system inputs: 3
             File system outputs: 1
             Socket messages sent: 0
             Socket messages received: 0
             Signals delivered: 1
             Page size (bytes): 4096
             Exit status: 0

File: time.info,  Node: Accuracy,  Next: Invoking time,  Prev: Examples,  Up: Resource Measurement

1.5 Accuracy
============

The elapsed time is not collected atomically with the execution of the
program; as a result, in bizarre circumstances (if the 'time' command
gets stopped or swapped out in between when the program being timed
exits and when 'time' calculates how long it took to run), it could be
much larger than the actual execution time.

   When the running time of a command is very nearly zero, some values
(e.g., the percentage of CPU used) may be reported as either zero (which
is wrong) or a question mark.

   Most information shown by 'time' is derived from the 'wait3' system
call.  The numbers are only as good as those returned by 'wait3'.  Many
systems do not measure all of the resources that 'time' can report on;
those resources are reported as zero.  The systems that measure most or
all of the resources are based on 4.2 or 4.3BSD. Later BSD releases use
different memory management code that measures fewer resources.

   On systems that do not have a 'wait3' call that returns status
information, the 'times' system call is used instead.  It provides much
less information than 'wait3', so on those systems 'time' reports most
of the resources as zero.

   The '%I' and '%O' values are allegedly only "real" input and output
and do not include those supplied by caching devices.  The meaning of
"real" I/O reported by '%I' and '%O' may be muddled for workstations,
especially diskless ones.

File: time.info,  Node: Invoking time,  Prev: Accuracy,  Up: Resource Measurement

1.6 Running the 'time' Command
==============================

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 (on the standard error output, by default).  If COMMAND exits
with non-zero status or is terminated by a signal, 'time' displays a
warning message and the exit status or signal number.

   Options to 'time' must appear on the command line before COMMAND.
Anything on the command line after COMMAND is passed as arguments to
COMMAND.

'-o FILE'
'--output=FILE'
     Write the resource use statistics to FILE.

'-a'
'--append'
     _Append_ the resource use information to the output file instead of
     overwriting it.

'-f FORMAT'
'--format=FORMAT'
     Use FORMAT as the format string.

'--help'
     Print a summary of the command line options to 'time' and exit.

'-p'
'--portability'
     Use the POSIX format.

'-v'
'--verbose'
     Use the built-in verbose format.

'-V'
'--version'
     Print the version number of 'time' and exit.

File: time.info,  Node: Concept index,  Prev: Resource Measurement,  Up: Top

Concept index
*************


* Menu:

* error (in measurement):                Accuracy.             (line  6)
* format:                                Format String.        (line  6)
* resource specifiers:                   Resource Measurement. (line 22)
* resources:                             Invoking time.        (line 10)
* time invocation:                       Resource Measurement. (line  6)
* verbose format:                        Setting Format.       (line 43)
* verbose option:                        Invoking time.        (line 42)
* version number:                        Invoking time.        (line 46)



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