 Example of time command | |
| Developer(s) | Various open-source and commercial developers |
|---|---|
| Operating system | Unix, Unix-like, Inferno |
| Platform | Cross-platform |
| Type | Command |
In computing, time is a command in Unix and Unix-like operating systems. It is used to determine the duration of execution of a particular command.
time(1) can exist as a standalone program (such as GNU time) or as a shell builtin in most cases (e.g. in sh, bash, tcsh or in zsh).
The total CPU time is the combination of the amount of time the CPU or CPUs spent performing some action for a program and the amount of time they spent performing system calls for the kernel on the program's behalf. When a program loops through an array, it is accumulating user CPU time. Conversely, when a program executes a system call such as exec or fork, it is accumulating system CPU time.
The term "real time" in this context refers to elapsed wall-clock time, like using a stop watch. The total CPU time (user time + sys time) may be more or less than that value. Because a program may spend some time waiting and not executing at all (whether in user mode or system mode) the real time may be greater than the total CPU time. Because a program may fork children whose CPU times (both user and sys) are added to the values reported by the time command, but on a multicore system these tasks are run in parallel, the total CPU time may be greater than the real time.
To use the command, simply precede any command by the word time, such as:
$timels When the command completes, time will report how long it took to execute the ls command in terms of user CPU time, system CPU time, and real time. The output format varies between different versions of the command, and some give additional statistics, as in this example:
$ timehostwikipedia.org wikipedia.org has address 103.102.166.224wikipedia.org mail is handled by 50 mx2001.wikimedia.org.wikipedia.org mail is handled by 10 mx1001.wikimedia.org.host wikipedia.org 0.04s user 0.02s system 7% cpu 0.780 total$time (either a standalone program, or when Bash shell is running in POSIX mode AND time is invoked as time -p) reports to standard error output.
Portable scripts should use time -p mode, which uses a different output format, but which is consistent with various implementations:
$ time-psha256sum/bin/ls 12477deb0e25209768cbd79328f943a7ea8533ece70256cdea96fae0ae34d1cc /bin/lsreal 0.00user 0.00sys 0.00$Current versions of GNU time, report more than just a time by default:
$ /usr/bin/timesha256sum/bin/ls 12477deb0e25209768cbd79328f943a7ea8533ece70256cdea96fae0ae34d1cc /bin/ls0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 2156maxresident)k0inputs+0outputs (0major+96minor)pagefaults 0swaps$Format of the output for GNU time, can be adjusted using TIME environment variable, and it can include information other than the execution time (i.e. memory usage). This behavior is not available in general POSIX-compliant time, or when executing as time -p.
Documentation of this time can be usually accessed using man 1 time.
According to the source code of the GNU implementation of time, most information shown by time is derived from the wait3 system call. On systems that do not have a wait3 call that returns status information, the times system call is used instead.
In a popular Unix shell Bash, time is a special keyword, that can be put before a pipeline (or single command), that measures time of entire pipeline, not just a singular (first) command, and uses a different default format, and puts empty line before reporting times:
$ timeseq10000000|wc-l 10000000real 0m0.078suser 0m0.116ssys 0m0.029s$The reported time is a time used by both seq and wc -l added up. Format of the output can be adjusted using TIMEFORMAT variable.
The time is not a builtin, but a special keyword, and can't be treated as a function or command. It also ignores pipeline redirections (even when executed as time -p, unless entire Bash is run in "POSIX mode").
Documentation of this time can be accessed using man 1 bash, or within bash itself using help time.
Bash, short for Bourne-Again SHell, is a shell program and command language supported by the Free Software Foundation and first developed for the GNU Project by Brian Fox. Designed as a 100% free software alternative for the Bourne shell, it was initially released in 1989. Its moniker is a play on words, referencing both its predecessor, the Bourne shell, and the concept of rebirth.
A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file manipulation, program execution, and printing text. A script which sets up the environment, runs the program, and does any necessary cleanup or logging, is called a wrapper.
A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts.
The Bourne shell (sh) is a shell command-line interpreter for computer operating systems.
In computing, ls is a command to list computer files and directories in Unix and Unix-like operating systems. It is specified by POSIX and the Single UNIX Specification.
The cd command, also known as chdir, is a command-line shell command used to change the current working directory in various operating systems. It can be used in shell scripts and batch files.
In Unix-like and some other operating systems, the pwd command writes the full pathname of the current working directory to the standard output.
In computing, a command is a directive to a computer program to perform a specific task. It may be issued via a command-line interface or as input to a network service as part of a network protocol, or as an event triggered in a graphical user interface.
In computing, a fork bomb is a denial-of-service (DoS) attack wherein a process continually replicates itself to deplete available system resources, slowing down or crashing the system due to resource starvation.
xargs is a command on Unix and most Unix-like operating systems used to build and execute commands from standard input. It converts input from standard input into arguments to a command.
In most Unix and Unix-like operating systems, the ps program displays the currently-running processes. The related Unix utility top provides a real-time view of the running processes.
In computing, echo is a command that outputs the strings that are passed to it as arguments. It is a command available in various operating system shells and typically used in shell scripts and batch files to output status text to the screen or a computer file, or as a source part of a pipeline.
The seven standard Unix file types are regular, directory, symbolic link, FIFO special, block special, character special, and socket as defined by POSIX. Different OS-specific implementations allow more types than what POSIX requires. A file's type can be identified by the ls -l command, which displays the type in the first character of the file-system permissions field.
In Unix-like operating systems, find is a command-line utility that locates files based on some user-specified criteria and either prints the pathname of each matched object or, if another action is requested, performs that action on each matched object.
A command shell is a command-line interface to interact with and manipulate a computer's operating system.
cpio is a general file archiver utility and its associated file format. It is primarily installed on Unix-like computer operating systems. The software utility was originally intended as a tape archiving program as part of the Programmer's Workbench (PWB/UNIX), and has been a component of virtually every Unix operating system released thereafter. Its name is derived from the phrase copy in and out, in close description of the program's use of standard input and standard output in its operation.
In computing, a shebang is the character sequence #!, consisting of the characters number sign and exclamation mark, at the beginning of a script. It is also called sharp-exclamation, sha-bang, hashbang, pound-bang, or hash-pling.
In Unix and Unix-like operating systems, job control refers to control of jobs by a shell, especially interactively, where a "job" is a shell's representation for a process group. Basic job control features are the suspending, resuming, or terminating of all processes in the job/process group; more advanced features can be performed by sending signals to the job. Job control is of particular interest in Unix due to its multiprocessing, and should be distinguished from job control generally, which is frequently applied to sequential execution.
The restricted shell is a Unix shell that restricts some of the capabilities available to an interactive user session, or to a shell script, running within it. It is intended to provide an additional layer of security, but is insufficient to allow execution of entirely untrusted software. A restricted mode operation is found in the original Bourne shell and its later counterpart Bash, and in the KornShell. In some cases a restricted shell is used in conjunction with a chroot jail, in a further attempt to limit access to the system as a whole.
In Unix and Unix-like operating systems, printf is a shell builtin that formats and outputs text like the same-named C function.
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