xfree86 man page for time

TIME(1)                                                       General Commands Manual                                                      TIME(1)

NAME
       time - run programs and summarize system resource usage

SYNOPSIS
       time   [ -apqvV ] [ -f FORMAT ] [ -o FILE ]
              [ --append ] [ --verbose ] [ --quiet ] [ --portability ]
              [ --format=FORMAT ] [ --output=FILE ] [ --version ]
              [ --help ] COMMAND [ ARGS ]

DESCRIPTION
       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
       status.

       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 used.

       Options to time must appear on the command line before COMMAND.  Anything on the command line after COMMAND is passed as arguments to
       COMMAND.

OPTIONS
       -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 file's previous contents.  This option is useful for collecting information on interactive programs and programs that produce
              output on the standard error stream.

       -a, --append
              Append the resource use information to the output file instead of overwriting it.  This option is only useful with the `-o' or
              `--output' option.

       -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.

       -p, --portability
              Use the following format string, for conformance with POSIX standard 1003.2:
                        real %e
                        user %U
                        sys %S

       -v, --verbose
              Use the built-in verbose format, which displays each available piece of information on the program's resource use on its own line,
              with an English description of its meaning.

       --quiet
              Do not report the status of the program even if it is different from zero.

       -V, --version
              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
       `--verbose', 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 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 printf(3) function.

       A backslash (`') introduces a `backslash escape', which is translated into a single printing character upon output.  `	' outputs a tab
       character, `
' 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 use
       information, so normally format strings do not end with a newline character (or `
').

       There are many resource specifications.  Not all resources are measured by all versions of Unix, so some of the values might be reported as
       zero.  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 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 timed.
              D      Average size of the process's unshared data area, in Kilobytes.
              E      Elapsed real (wall clock) time used by the process, in [hours:]minutes:seconds.
              F      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.
              I      Number of file system inputs by the process.
              K      Average total (data+stack+text) memory use of the process, in Kilobytes.
              M      Maximum resident set size of the process during its lifetime, 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 directly (in user mode), in seconds.
              W      Number of times the process was swapped out of main memory.
              X      Average amount of shared text in the process, in Kilobytes.
              Z      System's page size, in bytes.  This is a per-system constant, but varies between systems.
              c      Number of times the process was context-switched involuntarily (because the time slice expired).
              e      Elapsed real (wall clock) time used by the process, in seconds.
              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 operation to
                     complete.
              x      Exit status of the command.

EXAMPLES
       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 "	%E real,	%U user,	%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="	%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

ACCURACY
       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(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 information, 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
       `real' I/O reported by `%I' and `%O' may be muddled for workstations, especially diskless ones.

DIAGNOSTICS
       The time command returns when the program exits, stops, or is terminated by a signal.  If the program exited normally, the return value of
       time is the return value of the program it executed and measured.  Otherwise, the return value is 128 plus the number of the signal which
       caused the program to stop or terminate.
AUTHOR
       time was written by David MacKenzie.  This man page was added by Dirk Eddelbuettel <edd@debian.org>, the Debian GNU/Linux maintainer, for
       use by the Debian GNU/Linux distribution but may of course be used by others.

SEE ALSO
       tcsh(1), printf(3)

                                                                 Debian GNU/Linux                                                          TIME(1)