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KILL(1P) POSIX Programmer's Manual KILL(1P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.
NAME
kill - terminate or signal processes
SYNOPSIS
kill -s signal_name pid ...
kill -l [exit_status]
kill [-signal_name] pid ...
kill [-signal_number] pid ...
DESCRIPTION
The 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 IEEE Std 1003.1-2001 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.
OPTIONS
The kill utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, 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:
-l (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 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 IEEE Std 1003.1-2001) 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 sig-
nal_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.
-signal_name
Equivalent to -s signal_name.
-signal_number
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 table.
The effects of specifying any signal_number other than those listed in the table are undefined.
signal_number sig Value
0 0
1 SIGHUP
2 SIGINT
3 SIGQUIT
6 SIGABRT
9 SIGKILL
14 SIGALRM
15 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.
OPERANDS
The following operands shall be supported:
pid One of the following:
1. 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
IEEE Std 1003.1-2001. If the first pid operand is negative, it should be preceded by "--" to keep it from
being interpreted as an option.
2. A job control job ID (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.203, 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 Shell Execution Environment .
exit_status
A decimal integer specifying a signal number or the exit status of a process terminated by a signal.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of kill:
LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions
volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization variables used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables.
LC_CTYPE
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).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diagnostic messages written to stan-
dard error.
NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
When 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>
where the <signal_name> is in uppercase, without the SIG prefix, and the <separator> shall be either a <newline> or a
<space>. For the last signal written, <separator> shall be a <newline>.
When both the -l option and exit_status operand are specified, the symbolic name of the corresponding signal shall be
written in the following format:
"%s\n", <signal_name>
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 At least one matching process was found for each pid operand, and the specified signal was successfully processed
for at least one matching process.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Process 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");
the kill operates in a different environment and does not share the shell's understanding of job numbers.
EXAMPLES
Any of the commands:
kill -9 100 -165
kill -s kill 100 -165
kill -s KILL 100 -165
sends the SIGKILL signal to the process whose process ID is 100 and to all processes whose process group ID is 165,
assuming the sending process has permission to send that signal to the specified processes, and that they exist.
The System Interfaces volume of IEEE Std 1003.1-2001 and this volume of IEEE Std 1003.1-2001 do not require specific sig-
nal numbers for any signal_names. Even the - signal_number option provides symbolic (although numeric) names for signals.
If a process is terminated by a signal, its exit status indicates the signal that killed it, but the exact values are not
specified. The kill -l option, however, can be used to map decimal signal numbers and exit status values into the name of
a signal. The following example reports the status of a terminated job:
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
To send the default signal to a process group (say 123), an application should use a command similar to one of the fol-
lowing:
kill -TERM -123
kill -- -123
RATIONALE
The -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 histori-
cal 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
IEEE Std 1003.1-2001 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 ver-
sions 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,
IEEE Std 1003.1-2001 mandates that it is always considered the former by implementations that support the XSI option. It
also requires that conforming applications always use the "--" 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 Syn-
tax 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");
the kill operates in a different environment and does not understand how the shell has managed its job numbers.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language, ps, wait(), the System Interfaces volume of IEEE Std 1003.1-2001, kill(), the Base Definitions
volume of IEEE Std 1003.1-2001, <signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 http://www.open-
group.org/unix/online.html .
IEEE/The Open Group 2003 KILL(1P)
