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Linux / Unix Command: time
Command Library


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 output giving timing statistics about this program run. These statistics consist of (i) the elapsed real time between invocation and termination, (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)).  


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.





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 format string that can be specified using the -f option or the TIME environment variable.

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
real %e
user %U
sys %S
is used.  

The format string

The format is interpreted in the usual printf-like way. Ordinary characters 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) are supported.


Elapsed real time (in [hours:]minutes:seconds).
(Not in tcsh.) Elapsed real time (in seconds).
Total number of CPU-seconds that the process spent in kernel mode.
Total number of CPU-seconds that the process spent in user mode.
Percentage of the CPU that this job got, computed as (%U + %S) / %E.


Maximum resident set size of the process during its lifetime, in Kbytes.
(Not in tcsh.) Average resident set size of the process, in Kbytes.
Average total (data+stack+text) memory use of the process, in Kbytes.
Average size of the process's unshared data area, in Kbytes.
(Not in tcsh.) Average size of the process's unshared stack space, in Kbytes.
Average size of the process's shared text space, in Kbytes.
(Not in tcsh.) System's page size, in bytes. This is a per-system constant, but varies between systems.
Number of major page faults that occurred while the process was running. These are faults where the page has to be read in from disk.
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.
Number of times the process was swapped out of main memory.
Number of times the process was context-switched involuntarily (because the time slice expired).
Number of waits: times that the program was context-switched voluntarily, for instance while waiting for an I/O operation to complete.


Number of file system inputs by the process.
Number of file system outputs by the process.
Number of socket messages received by the process.
Number of socket messages sent by the process.
Number of signals delivered to the process.
(Not in tcsh.) Name and command line arguments of the command being timed.
(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.
-p, --portability
Use the portable output format.
-o FILE, --output=FILE
Do not send the results to stderr, but overwrite the specified file.
-a, --append
(Used together with -o.) Do not overwrite but append.
-v, --verbose
Give very verbose output about all the program knows about.


Print a usage message on standard output and exit successfully.
-V, --version
Print version information on standard output, then exit successfully.
Terminate option list.


tcsh(1), times(2), wait3(2)  

Important: Use the man command (% man) to see how a command is used on your particular computer.

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