time
CommandCopyright © 1989, 1991 Free Software Foundation, Inc.
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time
: Measuring Program Resource UsageThe 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 Formatting The Output), or have
time
save the information in a file instead of display it on the
screen (see section Using the time
command).
The format of the time
command is:
time [-apvV] [-f format] [-o file] [--append] [--portability] [--verbose] [--format=format] [--output-file=file] [--version] command [arg…]
Here is an example of using time
to measure the time and other
resources used by running the program a.out
:
time a.out
1.1 Using the time command | Running the time command, and its options.
| |
1.2 Formatting The Output | Selecting the information reported by time .
| |
1.3 Examples | Examples of using time .
| |
1.4 Accuracy | Limitations on the accuracy of time output.
|
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time
commandThe format of the time
command is:
time [-apvV] [-f format] [-o file] [--append] [--portability] [--verbose] [--format=format] [--output-file=file] [--version] command [arg…]
time
first runs the program command. 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, time
displays
a warning message and the exit status.
time
determines which information to display about the resources
used by the command from a format string (see section Formatting The Output).
If no format is specified on the command line, but the TIME
environment variable is set, its value is used as the format.
Otherwise, a default format built into time
is used
(see section Formatting The Output).
Options to time
must appear on the command line before
command. Anything on the command line after command is
passed as arguments to command.
The long-named options can be introduced with ‘+’ as well as ‘--’, for compatibility with previous releases. Eventually support for ‘+’ will be removed, because it is incompatible with the POSIX.2 standard.
Write the resource usage statistics to file instead of to the standard error stream. By default, this overwrites the file, destroying the file’s previous contents. This option is useful for collecting information on interactive programs and programs that produce output on the standard error stream.
Append the resource usage information to the output file instead of overwriting it. This option is only useful with the ‘-o’ or ‘--output-file’ option.
Use format as the format string that controls the output of
time
.
Use the following format string, for conformance with POSIX 1003.2:
real %e user %U sys %S
Use the built-in verbose format (different from the built-in default format), which displays every available piece of information on the program’s resource usage, on its own line with an English description of its meaning.
Print the version number of time
.
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The format string controls the contents of the time
output.
The format string can be set using the ‘-f’ or ‘--format’
options, or a built-in verbose format can be selected using the
‘-v’ or ‘--verbose’ options; if they are not given, but the
TIME
environment variable is set, its value is used as the format
string. Otherwise, a built-in default format is used. The default
format is:
%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k %Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
The format string usually consists of resource specifiers
interspersed with plain text. A percent sign (‘%’) in the format
string causes the following character to be interpreted as a resource
specifier, which is similar to the formatting characters in the C
printf
function.
A backslash (‘\’) introduces a backslash escape, which is translated into a single printing character upon output. ‘\t’ outputs a tab character, ‘\n’ outputs a newline, and ‘\\’ outputs a backslash. A backslash followed by any other character outputs a question mark (‘?’) followed by a backslash, to indicate that an invalid backslash escape was given.
Other text in the format string is copied verbatim to the output.
time
always prints a newline after printing the resource usage
information, so normally format strings do not end with a newline
character (or ‘\n’).
There are many resource specifications. Not all resources are measured by all versions of Unix, so some of the values might be reported as 0. Any character following a percent sign that is not listed in the table below causes a question mark (‘?’) to be output, followed by that character, to indicate that an invalid resource specifier was given.
The resource specification characters are:
A literal ‘%’.
The name and command line arguments of the command being timed.
The average size of the process’s unshared data area, in Kilobytes.
The elapsed real (wall clock) time used by the process, in [hours:]minutes:seconds.microseconds.
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.
Number of file system inputs by the process.
The average total memory usage of the process, in Kilobytes.
The maximum resident set size of the process during its lifetime, in Kilobytes.
Number of file system outputs by the process.
The percentage of the CPU that this job got. This is just user + system times divied by the total running time.
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.
Total number of CPU-seconds used by the system on behalf of the process (in kernel mode), in seconds:microseconds.
Total number of CPU-seconds that the process used directly (in user mode), in seconds:microseconds.
Number of times the process was swapped out of main memory.
Average amount of shared text in the process, in Kilobytes.
The system’s page size, in bytes. This is a per-system constant, but varies between systems.
Number of times the process was context-switched involuntarily (because the time slice expired).
The elapsed real (wall clock) time used by the process, in seconds.microseconds.
Number of signals delivered to the process.
The average unshared stack size of the process, in Kilobytes.
Number of socket messages received by the process.
Number of socket messages sent by the process.
The average resident set size of the process, in Kilobytes.
Number of times that the program was context-swapped voluntarily, for instance while waiting for an I/O operation to complete.
The exit status of the process.
The resource specification characters are a superset of those recognized
by the tcsh
builtin time
command.
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These examples assume that your command interpreter is bash
.
To run the command ‘wc /etc/hosts’ and show the default information:
time wc /etc/hosts
To run the command ‘ls -Fs’ and show just the user, system, and total time:
time -f "\t%E real,\t%U user,\t%S sys" ls -Fs
To edit the file bork and have time
append the elapsed time
and number of signals to the file ‘log’, reading the format string
from the environment variable TIME
:
export TIME="\t%E,\t%k" time -a -o log emacs bork
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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
. On systems that do not have a wait3
call that
returns status information, the times
system call is used
instead. However, it provides much less information than
wait3
, so on those systems time
reports the majority
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.
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