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kill(P) kill(P)
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 - sig-
nal_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() ) correspond-
ing 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 num-
ber, the signal_name (the symbolic constant name
without the SIG prefix defined in the Base Defi-
nitions volume of IEEE Std 1003.1-2001) corre-
sponding to that signal shall be written. Other-
wise, the results are unspecified.
-s signal_name
Specify the signal to send, using one of the sym-
bolic 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, sig-
nal_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 nega-
tive pid operand specifying a process group.
OPERANDS
The following operands shall be supported:
pid 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 cur-
rent 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.
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 sig-
naled. The job control job ID notation is applicable
only for invocations of kill in the current shell execu-
tion environment; see Shell Execution Environment .
exit_status
A decimal integer specifying a signal number or
the exit status of a process terminated by a sig-
nal.
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 internationaliza-
tion 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 internationalization variables
used to determine the values of locale cate-
gories.)
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 mes-
sages written to standard 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 suc-
cessfully 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 exam-
ples:
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 spe-
cific 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 sig-
nal 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
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 termi-
nal 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 for-
mat 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 sig-
nal_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
versions of kill have not written the SIG prefix for the
-l option and have not recognized the SIG prefix on sig-
nal_names. Since neither applications portability nor
ease-of-use would be improved by requiring this exten-
sion, 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 appli-
cations 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 exam-
ples:
nohup kill %1 &
system("kill %1");
the kill operates in a different environment and does
not understand how the shell has managed its job num-
bers.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language , ps , wait() , the System Inter-
faces 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 Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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 .
POSIX 2003 kill(P)
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