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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 .