time命令

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命令用途

time 命令用于测量 Linux 命令的执行时间，输出其实际运行时间（real）、用户态 CPU 时间（user）和内核态 CPU 时间（sys），帮助分析命令性能。

常用用法示例

1. 基本用法：测量命令执行时间

   time ls -l
   real 0m0.003s
   user 0m0.001s
   sys 0m0.002s

   测量 ls -l 命令的执行时间，输出各阶段耗时。

2. 测量长时间运行的命令

   time sleep 1
   real 0m1.002s
   user 0m0.001s
   sys 0m0.001s

   测量 sleep 1 的执行时间，real 接近 1 秒，而 CPU 占用极低。

3. 将输出重定向到文件

   /usr/bin/time -o output.txt ls
   output.txt 内容
   
   0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 1784maxresident)k
   0inputs+0outputs (0major+76minor)pagefaults 0swaps

   使用 /usr/bin/time 并将结果保存到 output.txt。

4. 测量脚本执行时间

   time ./script.sh
   real 0m0.123s
   user 0m0.045s
   sys 0m0.078s

   测量 Shell 脚本的总执行时间。

5. 结合管道命令测量

   time find / -name "*.txt" 2>/dev/null | wc -l
   real 0m2.456s
   user 0m0.234s
   sys 0m0.567s

   测量管道命令的总耗时（包含 find 和 wc）。

6. 多次运行取平均时间

   /usr/bin/time --verbose -f "%E" sleep 0.5 # 多次手动运行后计算
   0:00.50

   需手动多次运行取平均值（示例为单次输出）。

7. 测量内存使用情况

   /usr/bin/time -v python3 script.py
   Maximum resident set size (kbytes): 25600 # 输出片段

   使用 -v 参数显示内存占用等详细信息。

8. 与 timeout 命令结合使用

   time timeout 2s dd if=/dev/zero of=/dev/null
   real 0m2.003s # 2秒后被终止

   测量被 timeout 限制的命令执行时间。

常用参数选项

• -p, –portability
  使用 POSIX 兼容格式输出，例如 real 0.05。
• -v, –verbose
  显示详细信息（如内存、I/O 等），仅适用于 /usr/bin/time。
• -o FILE, –output=FILE
  将结果写入文件而非标准错误输出。
• -a, –append
  与 -o 配合使用，追加内容到文件而非覆盖。
• -f FORMAT, –format=FORMAT
  自定义输出格式（如 -f “Real: %E”）。
• –quiet
  禁止显示错误信息（如命令不存在）。
• -h, –help
  显示帮助信息。
• -V, –version
  显示版本信息。

原厂文档

NAME

       time - time a simple command or give resource usage

SYNOPSIS

       time [option ...] command [argument ...]

DESCRIPTION

       The time command runs the specified program command with the given
       arguments.  When command finishes, time writes a message to
       standard error 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)).

       Note: some shells (e.g., bash(1)) have a built-in time command
       that provides similar information on the usage of time and
       possibly other resources.  To access the real command, you may
       need to specify its pathname (something like /usr/bin/time).

OPTIONS

       -p     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.

EXIT STATUS

       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.

ENVIRONMENT

       The variables LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, LC_NUMERIC, and
       NLSPATH are used for the text and formatting of the output.  PATH
       is used to search for command.

GNU VERSION

       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 is used:

           real %e
           user %U
           sys %S

   The format string
       The format is interpreted in the usual printf(3)-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.

       Time

       %E     Elapsed real time (in [hours:]minutes:seconds).

       %e     (Not in tcsh(1).)  Elapsed real time (in seconds).

       %S     Total number of CPU-seconds that the process spent in
              kernel mode.

       %U     Total number of CPU-seconds that the process spent in user
              mode.

       %P     Percentage of the CPU that this job got, computed as (%U +
              %S) / %E.

       Memory

       %M     Maximum resident set size of the process during its
              lifetime, in Kbytes.

       %t     (Not in tcsh(1).)  Average resident set size of the
              process, in Kbytes.

       %K     Average total (data+stack+text) memory use of the process,
              in Kbytes.

       %D     Average size of the process's unshared data area, in
              Kbytes.

       %p     (Not in tcsh(1).)  Average size of the process's unshared
              stack space, in Kbytes.

       %X     Average size of the process's shared text space, in Kbytes.

       %Z     (Not in tcsh(1).)  System's page size, in bytes.  This is a
              per-system constant, but varies between systems.

       %F     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.

       %R     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.

       %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 waits: times that the program was context-
              switched voluntarily, for instance while waiting for an I/O
              operation to complete.

       I/O

       %I     Number of filesystem inputs by the process.

       %O     Number of filesystem 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.

       %C     (Not in tcsh(1).)  Name and command-line arguments of the
              command being timed.

       %x     (Not in tcsh(1).)  Exit status of the command.

   GNU options
       -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.

       -q, --quiet
              Don't report abnormal program termination (where command is
              terminated by a signal) or nonzero exit status.

   GNU standard options
       --help Print a usage message on standard output and exit
              successfully.

       -V, --version
              Print version information on standard output, then exit
              successfully.

       --     Terminate option list.

BUGS

       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 requirements.

       The environment variable TIME was badly chosen.  It is not unusual
       for systems like autoconf(1) or make(1) 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 pathnames) 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 bug-time@gnu.org.
       Please include the version of time, which you can get by running

           time --version

       and the operating system and C compiler you used.

SEE ALSO

       bash(1), tcsh(1), times(2), wait3(2)

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