Measure the running time of a program.
The `time’ command will run another program, and record the elapsed time or CPU Resource Used time used by that program.
The information mmay be displayed on screen or saved in a file.
Syntax time [option...] command [arg...] Options -o FILE --output=FILE Write the resource use statistics to FILE. -a --append *Append* the resource use information to the output file instead of overwriting it. -f FORMAT --format=FORMAT Use FORMAT as the format string, see below for formatting options. --help Summary of the command line options. -o FILE --output=FILE Write the resource use statistics to FILE. By default, this *overwrites* the file, destroying the file's previous contents. -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. -p --portability Use the POSIX format. -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. -V --version Print the version number of `time' and exit. Options to `time' must appear on the command line before COMMAND. Anything on the command line after COMMAND is passed as arguments to COMMAND.
Setting the Output Format
`time’ uses a “format string” to determine which information to display about the resources used by the command it runs. You can specify a format string with the options listed above.
If no format is specified on the command line, but the `TIME’ environment variable is set, its value is used as the format string. Otherwise, the default format built into `time’ is used:
%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k %Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
The Format String
The “format string” controls the contents of the `time’ output. It consists of “resource specifiers” and “escapes”, interspersed with
A backslash introduces an “escape”, which is translated into a single printing character upon output. The valid escapes are listed
below. An invalid escape is output as a question mark followed by a backslash.\t a tab character \n a newline \\ a literal backslash
`time’ always prints a newline after printing the resource use information, so normally format strings do not end with a newline
character (or `\n’).
A resource specifier consists of a percent sign followed by another character. An invalid resource specifier is output as a question mark
followed by the invalid character. Use `%%’ to output a literal percent sign.
%E Elapsed real (wall clock) time used by the process, in [hours:]minutes:seconds. %e Elapsed real (wall clock) time used by the process, in seconds. %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. %P Percentage of the CPU that this job got. This is just user + system times divied by the total running time. Memory Resources %M Maximum resident set size of the process during its lifetime, in Kilobytes. %t Average resident set size of the process, in Kilobytes. %K Average total (data+stack+text) memory use of the process, in Kilobytes. %D Average size of the process's unshared data area, in Kilobytes. %p Average size of the process's unshared stack, in Kilobytes. %X Average size of the process's shared text, in Kilobytes. %Z System's page size, in bytes. This is a per-system constant, but varies between systems. I/O Resources %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. %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. %W Number of times the process was swapped out of main memory. %c Number of times the process was context-switched involuntarily (because the time slice expired). %w Number of times that the program was context-switched voluntarily, for instance while waiting for an I/O operation to complete. %I Number of file system inputs by the process. %O Number of file system outputs by the process. %r Number of socket messages received by the process. %s Number of socket messages sent by the process. %k Number of signals delivered to the process. Command Info %C Name and command line arguments of the command being timed. %x Exit status of the command. Examples Run the command `wc /etc/hosts' and show the default information: $ time wc /etc/hosts 35 111 1134 /etc/hosts 0.00user 0.01system 0:00.04elapsed 25%CPU (0avgtext+0avgdata 0maxresident)k 1inputs+1outputs (0major+0minor)pagefaults 0swaps Run the command `ls -Fs' and show the user, system, and wall-clock time: $ time -f "\t%E real,\t%U user,\t%S sys" ls -Fs total 16 1 account/ 1 db/ 1 mail/ 1 run/ 1 backups/ 1 emacs/ 1 msgs/ 1 rwho/ 1 crash/ 1 games/ 1 preserve/ 1 spool/ 1 cron/ 1 log/ 1 quotas/ 1 tmp/ 0:00.03 real, 0.00 user, 0.01 sys Run the command `cat' and record the elapsed time (stopwatch) until `cat' is closed with Ctrl-D $ time cat ^d 0:16.55, 726
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