time - run programs and summarize system resource usage
time [ -apqvV ] [ -f FORMAT ] [ -o FILE ]
[ --append ] [ --verbose ] [ --quiet ] [ --portability ]
[ --format=FORMAT ] [ --output=FILE ] [ --version ]
[ --help ] COMMAND [ ARGS ]
time run 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, time displays a warning message and the exit sta
time determines which information to display about the resources used
by the COMMAND from the string FORMAT. 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
Options to time must appear on the command line before COMMAND. Any
thing on the command line after COMMAND is passed as arguments to COM
-o FILE, --output=FILE
Write the resource use statistics to FILE instead of to the
standard error stream. By default, this overwrites the file,
destroying the files 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 use information to the output file instead
it. This option is only useful with the -o or --output op
-f FORMAT, --format FORMAT
Use FORMAT as the format string that controls the output of
time. See the below more information.
--help Print a summary of the command line options and exit.
Use the following format string, for conformance with POSIX
Use the built-in verbose format, which displays each available
piece of information on the programs resource use on its own
line, with an English description of its meaning.
Do not report the status of the program even if it is different
Print the version number of time and exit.
FORMATTING THE OUTPUT
The format string FORMAT controls the contents of the time output. The
format string can be set using the -f or --format, -v or --ver
bose, or -p or --portability 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
%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
%Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
The format string usually consists of resource specifiers inter
spersed with plain text. A percent sign (%) in the format string
causes the following character to be interpreted as a resource specifi
er, which is similar to the formatting characters in the printf(3)
A backslash (\) introduces a backslash escape, which is translated
into a single printing character upon output. \t outputs a tab char
acter, \n outputs a newline, and \\ outputs a backslash. A back
slash followed by any other character outputs a question mark (?)
followed by a backslash, to indicate that an invalid backslash escape
Other text in the format string is copied verbatim to the output. time
always prints a newline after printing the resource use information, so
normally format strings do not end with a newline character (or 0).
There are many resource specifications. Not all resources are measured
by all versions of Unix, so some of the values might be reported as ze
ro. 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 listed in the table be
low causes a question mark (?) to be output, followed by that charac
ter, to indicate that an invalid resource specifier was given.
The resource specifiers, which are a superset of those recognized by
the tcsh(1) builtin time command, are:
% A literal %.
C Name and command line arguments of the command being
D Average size of the processs unshared data area, in
E Elapsed real (wall clock) time used by the process, in
F Number of major, or I/O-requiring, page faults that oc
curred while the process was running. These are faults
where the page has actually migrated out of primary memo
I Number of file system inputs by the process.
K Average total (data+stack+text) memory use of the pro
cess, in Kilobytes.
M Maximum resident set size of the process during its life
time, in Kilobytes.
O Number of file system outputs by the process.
P Percentage of the CPU that this job got. This is just
user + system times divided by the total running time. It
also prints a percentage sign.
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.
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 direct
ly (in user mode), in seconds.
W Number of times the process was swapped out of main memo
X Average amount of shared text in the process, in Kilo
Z Systems page size, in bytes. This is a per-system con
stant, but varies between systems.
c Number of times the process was context-switched involun
tarily (because the time slice expired).
e Elapsed real (wall clock) time used by the process, in
k Number of signals delivered to the process.
p Average unshared stack size of the process, in Kilobytes.
r Number of socket messages received by the process.
s Number of socket messages sent by the process.
t Average resident set size of the process, in Kilobytes.
w Number of times that the program was context-switched
voluntarily, for instance while waiting for an I/O opera
tion to complete.
x Exit status of the command.
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 -f "%E real,%U user,%S sys" ls -Fs
To edit the file BORK and have time append the elapsed time and num
ber of signals to the file log, reading the format string from the
environment variable TIME:
export TIME="%E,%k" # If using bash or ksh
setenv TIME "%E,%k" # If using csh or tcsh
time -a -o log emacs bork
Users of the bash shell need to use an explicit path in order to run
the external time command and not the shell builtin variant. On system
where time is installed in /usr/bin, the first example would become
/usr/bin/time wc /etc/hosts
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 ex
its 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(2) system
call. The numbers are only as good as those returned by wait3(2). On
systems that do not have a wait3(2) call that returns status informa
tion, the times(2) system call is used instead. However, it provides
much less information than wait3(2), 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 re
al I/O reported by %I and %O may be muddled for workstations, es
pecially diskless ones.
The time command returns when the program exits, stops, or is terminat
ed by a signal. If the program exited normally, the return value of
time is the return value of the program it executed and measured. Oth
erwise, the return value is 128 plus the number of the signal which
caused the program to stop or terminate.
time was written by David MacKenzie. This man page was added by Dirk
Eddelbuettel , the Debian GNU/Linux maintainer, for use
by the Debian GNU/Linux distribution but may of course be used by oth
Debian GNU/Linux TIME(1)