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)).
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 nonzero value (1-125) if
something 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 format string that can be
specified using the -f option or the TIME environment variable.
The default format string is
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
Total number of CPU-seconds that the process spent in user
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
Average total (data+stack+text) memory use of the process,
Average size of the process's unshared data area, in
(Not in tcsh.) Average size of the process's unshared stack
space, in Kbytes.
Average size of the process's shared text space, in
(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
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
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 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
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 path names) 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