Kill (command)

Implementations

Unix and Unix-like

There are many different signals that can be sent (see signal for a full list), although the signals in which users are generally most interested 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.

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. The two exceptions 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.

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.

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

kill 1234 kill -s TERM 1234 kill -TERM 1234 kill -15 1234

The process can be sent a SIGKILL signal in three ways:

kill -s KILL 1234 kill -KILL 1234 kill -9 1234

Other useful signals include HUP, TRAP, INT and ALRM. HUP sends the SIGHUP signal. Some daemons, including Apache and Sendmail, re-read configuration files upon receiving SIGHUP, so the kill command may be used for this too. A SIGINT signal can be generated very simply by pressing in most Unix shells. It is also common for to be mapped to SIGTSTP, and for (backslash) to be mapped to SIGQUIT, which can force a program to do a core dump.

Related programs

Microsoft Windows

Microsoft Windows XP, Vista and 7 include the command taskkill to terminate processes. An "unsupported" version of kill was included in several releases of the Microsoft Windows Resource Kits (aka "RezKits") available for Windows NT 3.x, NT 4.0, Windows 2000 and Microsoft Windows Server 2003, the most efficacious of these being Version 3.5 of Kill, Copyright (C) 1994 Microsoft Corp.

GNU versions of kill have been ported via Cygwin and run inside of the Unix environment subsystem that Microsoft Windows Services for UNIX provides (Microsoft acquired Windows Services for Unix wholesale via their purchase of Softway Systems and their Interix product on September 17, 1999).

Examples

PS C:\>ps p* | where { $_.Company -like "Microsoft*" -and $_.WorkingSet -gt 10MB } | kill -confirm

Confirm Are you sure you want to perform this action? Performing operation "Stop-Process" on Target "powershell (6832)". [Y] Yes [A] Yes to All [N] No [L] No to All [S] Suspend [?] Help (default is "Y"): n PS C:\>

Microsoft Singularity

Examples

Singularity>kill SampleProcess Cannot find active process Name=SampleProcess

Stop the process with the process identifier "42":

Singularity>kill 42 Cannot find active process ID=42

Plan 9 from Bell Labs

A similar command provided is called slay, which does the same but for processes that refuse to be killed this way.

Examples

kill troff | rc

See also

References

External links

Category:Unix SUS2008 utilities Category:Unix process and task management-related software Category:Process (computing) Category:Windows administration