man > 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.  `\t' outputs a tab  character,  `\n'  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 `\n').

       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 "\t%E real,\t%U user,\t%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="\t%E,\t%k" # If using bash or ksh
            setenv TIME "\t%E,\t%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 AT 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)