kill(1p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

KILL(1P)                POSIX Programmer's Manual               KILL(1P)

PROLOG         top

       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         top

       kill — terminate or signal processes

SYNOPSIS         top

       kill -s signal_name pid...

       kill -l [exit_status]

       kill [-signal_name] pid...

       kill [-signal_number] pid...

DESCRIPTION         top

       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         top

       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         top

       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         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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         top

       Default.

STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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         top

       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         top

       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         top

       None.

SEE ALSO         top

       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)

COPYRIGHT         top

       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)

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