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KILL(1P) POSIX Programmer's Manual KILL(1P)
This 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.
kill — terminate or signal processes
kill -s signal_name pid...
kill -l [exit_status]
kill [-signal_name] pid...
kill [-signal_number] pid...
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 POSIX.1‐2017 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.
The kill utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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 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.1‐2017) 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.
-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 list.
The effects of specifying any signal_number other than
those listed below are undefined.
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.
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 POSIX.1‐2017. 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 POSIX.1‐2017, 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.
exit_status
A decimal integer specifying a signal number or the exit
status of a process terminated by a signal.
Not used.
None.
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 POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization 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
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
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>
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
The following sections are informative.
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.
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 POSIX.1‐2017 and this volume of
POSIX.1‐2017 do not require specific signal 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 following:
kill -TERM -123
kill -- -123
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 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.1‐2017 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 "--" 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");
the kill operates in a different environment and does not
understand how the shell has managed its job numbers.
None.
Chapter 2, Shell Command Language, ps(1p), wait(1p)
The Base Definitions volume of POSIX.1‐2017, Section 3.204, Job
Control Job ID, Chapter 8, Environment Variables, Section 12.2,
Utility Syntax Guidelines, signal.h(0p)
The System Interfaces volume of POSIX.1‐2017, kill(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 KILL(1P)
Pages that refer to this page: signal.h(0p), bg(1p), fg(1p), jobs(1p), ps(1p), qdel(1p), qsig(1p), wait(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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