time - time a simple command or give resource usage
time [options] command [arguments...]
The time command runs the specified program command with the given
arguments. When command finishes, time writes a message to standard
error giving timing statistics about this program run. These statis-
tics consist of (i) the elapsed real time between invocation and termi-
nation, (ii) the user CPU time (the sum of the tms_utime and tms_cutime
values in a struct tms as returned by times(2)), and (iii) the system
CPU time (the sum of the tms_stime and tms_cstime values in a struct
tms as returned by times(2)).
Note: some shells (e.g., bash(1)) have a built-in time command that
provides less functionality than the command described here. To access
the real command, you may need to specify its pathname (something like
-p When in the POSIX locale, use the precise traditional format
"real %f\nuser %f\nsys %f\n"
(with numbers in seconds) where the number of decimals in the
output for %f is unspecified but is sufficient to express the
clock tick accuracy, and at least one.
The variables LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, LC_NUMERIC, NLSPATH
and PATH are used. The last one to search for command. The remaining
ones for the text and formatting of the output.
If command was invoked, the exit status is that of command. Otherwise
it is 127 if command could not be found, 126 if it could be found but
could not be invoked, and some other non-zero value (1-125) if some-
thing else went wrong.
Below a description of the GNU 1.7 version of time. Disregarding the
name of the utility, GNU makes it output lots of useful information,
not only about time used, but also on other resources like memory, I/O
and IPC calls (where available). The output is formatted using a for-
mat string that can be specified using the -f option or the TIME envi-
The default format string is
%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
%Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
When the -p option is given the (portable) output format
The format string
The format is interpreted in the usual printf-like way. Ordinary char-
acters are directly copied, tab, newline and backslash are escaped
using \t, \n and \\, a percent sign is represented by %%, and otherwise
% indicates a conversion. The program time will always add a trailing
newline itself. The conversions follow. All of those used by tcsh(1)
%E Elapsed real time (in [hours:]minutes:seconds).
%e (Not in tcsh.) Elapsed real time (in seconds).
%S Total number of CPU-seconds that the process spent in kernel
%U Total number of CPU-seconds that the process spent in user mode.
%P Percentage of the CPU that this job got, computed as (%U + %S) /
%M Maximum resident set size of the process during its lifetime, in
%t (Not in tcsh.) Average resident set size of the process, in
%K Average total (data+stack+text) memory use of the process, in
%D Average size of the process's unshared data area, in Kbytes.
%p (Not in tcsh.) Average size of the process's unshared stack
space, in Kbytes.
%X Average size of the process's shared text space, in Kbytes.
%Z (Not in tcsh.) System's page size, in bytes. This is a per-sys-
tem constant, but varies between systems.
%F Number of major page faults that occurred while the process was
running. These are faults where the page has to be read in from
%R Number of minor, or recoverable, page faults. These are faults
for pages that are not valid 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 waits: times that the program was context-switched
voluntarily, for instance while waiting for an I/O operation to
%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.
%C (Not in tcsh.) Name and command line arguments of the command
%x (Not in tcsh.) Exit status of the command.
-f FORMAT, --format=FORMAT
Specify output format, possibly overriding the format specified
in the environment variable TIME.
Use the portable output format.
-o FILE, --output=FILE
Do not send the results to stderr, but overwrite the specified
(Used together with -o.) Do not overwrite but append.
Give very verbose output about all the program knows about.
GNU STANDARD OPTIONS
--help Print a usage message on standard output and exit successfully.
Print version information on standard output, then exit success-
-- Terminate option list.
Not all resources are measured by all versions of Unix, so some of the
values might be reported as zero. The present selection was mostly
inspired by the data provided by 4.2 or 4.3BSD.
GNU time version 1.7 is not yet localized. Thus, it does not implement
the POSIX requirements.
The environment variable TIME was badly chosen. It is not unusual for
systems like autoconf or make to use environment variables with the
name of a utility to override the utility to be used. Uses like MORE or
TIME for options to programs (instead of program pathnames) tend to
lead to difficulties.
It seems unfortunate that -o overwrites instead of appends. (That is,
the -a option should be the default.)
Mail suggestions and bug reports for GNU time to
Please include the version of time, which you can get by running
and the operating system and C compiler you used.
tcsh(1), times(2), wait3(2)
POSIXization, autoconfiscation, GNU getoptization, docu-
mentation, other bug fixes and improvements.
Arne Henrik Juul
Helped with portability
Helped with portability