PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAMEkill --- terminate or signal processes
kill -s signal_name pid... kill -l [exit_status] kill [-signal_name] pid... kill [-signal_number] pid...
DESCRIPTIONThe kill utility shall send a signal to the process or processes specified by each pid operand. For each pid operand, the kill utility shall perform actions equivalent to the kill() function defined in the System Interfaces volume of POSIX.1-2008 called with the following arguments:
- The value of the pid operand shall be used as the pid argument.
- The sig argument is the value specified by the -s option, -signal_number option, or the -signal_name option, or by SIGTERM, if none of these options is specified.
OPTIONSThe kill utility shall conform to the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines, except that in the last two SYNOPSIS forms, the -signal_number and -signal_name options are usually more than a single character. The following options shall be supported:
- (The letter ell.) Write all values of signal_name supported by the implementation, if no operand is given. If an exit_status operand is given and it is a value of the '?' shell special parameter (see Section 2.5.2, Special Parameters and wait) corresponding to a process that was terminated by a signal, the signal_name corresponding to the signal that terminated the process shall be written. If an exit_status operand is given and it is the unsigned decimal integer value of a signal number, the signal_name (the symbolic constant name without the SIG prefix defined in the Base Definitions volume of POSIX.1-2008) corresponding to that signal shall be written. Otherwise, the results are unspecified.
- -s signal_name
Specify the signal to send, using one of the symbolic names defined in the <signal.h> header. Values of signal_name shall be recognized in a case-independent fashion, without the SIG prefix. In addition, the symbolic name 0 shall be recognized, representing the signal value zero. The corresponding signal shall be sent instead of SIGTERM.
Equivalent to -s signal_name.
Specify a non-negative decimal integer, signal_number, representing the signal to be used instead of SIGTERM, as the sig argument in the effective call to kill(). The correspondence between integer values and the sig value used is shown in the following list.
The effects of specifying any signal_number other than those listed below are undefined.
- SIGTERM If the first argument is a negative integer, it shall be interpreted as a -signal_number option, not as a negative pid operand specifying a process group.
OPERANDSThe following operands shall be supported:
One of the following:
- A decimal integer specifying a process or process group to be signaled. The process or processes selected by positive, negative, and zero values of the pid operand shall be as described for the kill() function. If process number 0 is specified, all processes in the current process group shall be signaled. For the effects of negative pid numbers, see the kill() function defined in the System Interfaces volume of POSIX.1-2008. If the first pid operand is negative, it should be preceded by dq--dq to keep it from being interpreted as an option.
- A job control job ID (see the Base Definitions volume of POSIX.1-2008, Section 3.204, Job Control Job ID) that identifies a background process group to be signaled. The job control job ID notation is applicable only for invocations of kill in the current shell execution environment; see Section 2.12, Shell Execution Environment.
- A decimal integer specifying a signal number or the exit status of a process terminated by a signal.
ENVIRONMENT VARIABLESThe following environment variables shall affect the execution of kill:
- Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2008, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- Determine the location of message catalogs for the processing of LC_MESSAGES.
STDOUTWhen the -l option is not specified, the standard output shall not be used. When the -l option is specified, the symbolic name of each signal shall be written in the following format:
"%s%c", <signal_name>, <separator>
STDERRThe standard error shall be used only for diagnostic messages.
EXIT STATUSThe following exit values shall be returned:
- At least one matching process was found for each pid operand, and the specified signal was successfully processed for at least one matching process.
- An error occurred.
CONSEQUENCES OF ERRORSDefault.
The following sections are informative.
APPLICATION USAGEProcess numbers can be found by using ps. The job control job ID notation is not required to work as expected when kill is operating in its own utility execution environment. In either of the following examples:
nohup kill %1 & system("kill %1");
EXAMPLESAny of the commands:
kill -9 100 -165 kill -s kill 100 -165 kill -s KILL 100 -165
job stat=$? if [ $stat -eq 0 ] then echo job completed successfully. elif [ $stat -gt 128 ] then echo job terminated by signal SIG$(kill -l $stat). else echo job terminated with error code $stat. fi
kill -TERM -123 kill -- -123
RATIONALEThe -l option originated from the C shell, and is also implemented in the KornShell. The C shell output can consist of multiple output lines because the signal names do not always fit on a single line on some terminal screens. The KornShell output also included the implementation-defined signal numbers and was considered by the standard developers to be too difficult for scripts to parse conveniently. The specified output format is intended not only to accommodate the historical C shell output, but also to permit an entirely vertical or entirely horizontal listing on systems for which this is appropriate. An early proposal invented the name SIGNULL as a signal_name for signal 0 (used by the System Interfaces volume of POSIX.1-2008 to test for the existence of a process without sending it a signal). Since the signal_name 0 can be used in this case unambiguously, SIGNULL has been removed. An early proposal also required symbolic signal_names to be recognized with or without the SIG prefix. Historical versions of kill have not written the SIG prefix for the -l option and have not recognized the SIG prefix on signal_names. Since neither applications portability nor ease-of-use would be improved by requiring this extension, it is no longer required. To avoid an ambiguity of an initial negative number argument specifying either a signal number or a process group, POSIX.1-2008 mandates that it is always considered the former by implementations that support the XSI option. It also requires that conforming applications always use the dq--dq options terminator argument when specifying a process group, unless an option is also specified. The -s option was added in response to international interest in providing some form of kill that meets the Utility Syntax Guidelines. The job control job ID notation is not required to work as expected when kill is operating in its own utility execution environment. In either of the following examples:
nohup kill %1 & system("kill %1");
SEE ALSOChapter 2, Shell Command Language, ps, wait The Base Definitions volume of POSIX.1-2008, Section 3.204, Job Control Job ID, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines, <signal.h> The System Interfaces volume of POSIX.1-2008, kill()
COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at www.unix.org/online.html .
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