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In Unix and Unix-like operating systems, kill is a command used to send simple messages to processes running on the system. By default, the message sent is the "termination" signal, which requests that the process exit. But kill is something of a misnomer; the signal sent may have nothing to do with process killing. The kill command is a wrapper around the kill() system call, which sends signals to processes or process groups on the system, referenced by their numeric process IDs (PIDs) or process group IDs (PGIDs). kill is always provided as a standalone utility, but most shells have built-in kill commands that may slightly differ from it. Wikipedia does not have an article with this exact name. ...
Jump to: navigation, search It has been suggested that List of Unixes be merged into this article or section. ...
Jump to: navigation, search A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ...
Jump to: navigation, search In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ...
In computing, a process is, roughly speaking, a task being run by a computer, often simultaneously with many other tasks. ...
A signal is an asynchronous event transmitted between one process and another. ...
In computer science, a wrapper is a piece of code which is combined with another piece of code to determine how that code is executed. ...
In computing, a system call, or software interrupt is the mechanism used by an application program to request service from the operating system. ...
A signal is an asynchronous event transmitted between one process and another. ...
In computing, the process identifier (normally referred to as the process ID or just PID) is a number used by some operating system kernels (such as that of UNIX or Windows NT) to uniquely identify a process. ...
Jump to: navigation, search A Unix shell, also called the command line, provides the traditional user interface for the Unix operating system. ...
There are many different signals that can be sent (see signal for a full list), although the signals that users are generally most interested in are SIGTERM and SIGKILL. The default signal sent is SIGTERM. Programs that handle this signal can do useful cleanup operations (such as saving configuration information to a file) before quitting. However, many programs do not implement a special handler for this signal, and so a default signal handler is called instead. Other times, even a process that has a special handler has gone awry in a way that prevents it from properly handling the signal. A signal is an asynchronous event transmitted between one process and another. ...
All signals except for SIGKILL and SIGSTOP can be "intercepted" by the process, meaning that a special function can be called when the program receives those signals. However, SIGKILL and SIGSTOP are only seen by the host system's kernel, providing reliable ways of controlling the execution of processes. SIGKILL kills the process, and SIGSTOP pauses it until a SIGCONT is received. The word kernel has a a variety of meanings in a several fields. ...
Unix provides security mechanisms to prevent unauthorized users from killing other processes. Essentially, for a process to send a signal to another, the owner of the signaling process must be the same as the owner of the receiving process or be the superuser. On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ...
The available signals all have different names, and are mapped to certain numbers. It is important to note that the specific mapping between numbers and signals can vary between Unix implementations. SIGTERM is often numbered 15 while SIGKILL is often numbered 9.
Examples
A process can be sent a SIGTERM signal in three ways (the process ID is '1234' in this case): kill 1234kill -TERM 1234kill -15 1234 The process can be sent a SIGKILL signal in two ways: kill -KILL 1234kill -9 1234 Other useful signals include HUP, TRAP, INT and ALRM. A SIGINT signal can be generated very simply by pressing CTRL+C in most Unix shells. It is also common for CTRL+Z to be mapped to SIGTSTP, and for CTRL+ (backslash) to be mapped to SIGQUIT, which can force a program to do a core dump. Jump to: navigation, search A Unix shell, also called the command line, provides the traditional user interface for the Unix operating system. ...
A core dump is a file containing the contents of memory at the time a program or computer crashed. ...
killall A related program is killall. On some variations of Unix, such as Solaris, this utility is automatically invoked when the system is going through a shutdown. It behaves much like the kill command above, but instead of sending a signal to an individual process, the signal is sent to all processes on the system. However, on others such as IRIX, Linux, and FreeBSD, an argument is supplied specifying the name of the process (or processes) to kill. For instance, to kill a process such as an instance of the XMMS music player invoked by xmms, the user would run the command killall xmms. This would kill all processes named xmms. Jump to: navigation, search An X-Ray image of the sun. ...
The phrase shut down, shut-down or shutdown can be used to mean turning off something, but most commonly used for machines, especially nuclear reactors and computers. ...
IRIX 6. ...
Jump to: navigation, search Tux, a cartoon penguin frequently featured sitting, is the official Linux mascot. ...
Jump to: navigation, search FreeBSD is a free, open source, Unix-like operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD) branch through 386BSD and 4. ...
XMMSs default appearance The X Multimedia System (XMMS) is a free audio player very similar to Winamp, that runs on many Unix-like operating systems. ...
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