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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.1‐2008 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.
The 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:
−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.1‐2008)
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.
−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.1‐2008. 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.1‐2008, 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.
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.1‐2008, 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.1‐2008 and this volume of
POSIX.1‐2008 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.1‐2008 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 "−−" 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.1‐2008, 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.1‐2008, kill(3p)
Portions 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 http://www.unix.org/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 2013 KILL(1P)
Pages that refer to this page: bg(1p), fg(1p), jobs(1p), ps(1p), qdel(1p), qsig(1p), wait(1p)
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