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PROLOG

       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.

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 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.

OPTIONS

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.

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 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.

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 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.

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 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

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 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.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       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(1POSIX)