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man pages section 1: User Commands

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Updated: Thursday, June 13, 2019
 
 

kill(1)

Name

kill - terminate or signal processes

Synopsis

/usr/bin/kill -s signal_name pid...
/usr/bin/kill -l [exit_status]
/usr/bin/kill [-signal_name] pid...
/usr/bin/kill [-signal_number] pid...

Description

The kill utility sends a signal to the process or processes specified by each pid operand.

For each pid operand, the kill utility performs actions equivalent to the kill(2) function called with the following arguments:

  1. The value of the pid operand is used as the pid argument.

  2. The sig argument is the value specified by the –s option, the signal_name option, or the signal_number option, or, if none of these options is specified, by SIGTERM.

The signaled process must belong to the current user unless the user is the super-user.

See NOTES for descriptions of the shell built-in versions of kill.

Options

The following options are supported:

–l

(The letter ell.) Writes all values of signal_name supported by the implementation, if no operand is specified. If an exit_status operand is specified and it is a value of the ? shell special parameter and wait corresponding to a process that was terminated by a signal, the signal_name corresponding to the signal that terminated the process is written. If an exit_status operand is specified and it is the unsigned decimal integer value of a signal number, the signal_name corresponding to that signal is written. Otherwise, the results are unspecified.

–s signal_name

Specifies the signal to send, using one of the symbolic names defined in the <signal.h> description. Values of signal_name is recognized in a case-independent fashion, without the SIG prefix. In addition, the symbolic name 0 is recognized, representing the signal value zero. The corresponding signal is sent instead of SIGTERM.

signal_name

Equivalent to –s signal_name.

signal_number

Specifies 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(2).

Operands

The following operands are 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 is as described for the kill function. If process number 0 is specified, all processes in the process group are signaled. 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 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.

The job control job ID type of pid is available only on systems supporting the job control option.

exit_status

A decimal integer specifying a signal number or the exit status of a process terminated by a signal.

Usage

Process numbers can be found by using ps(1).

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:

example% nohup kill %1 &
example% system( "kill %1");

kill operates in a different environment and does not share the shell's understanding of job numbers.

OUTPUT

When the –l option is not specified, the standard output is not be used.

When the –l option is specified, the symbolic name of each signal is written in the following format:

"%s%c", <signal_name>, <separator>

where the <signal_name> is in upper-case, without the SIG prefix, and the <separator> is either a newline character or a space character. For the last signal written, <separator> is a newline character.

When both the –l option and exit_status operand are specified, the symbolic name of the corresponding signal is written in the following format:

"%s\n", <signal_name>

Examples

Example 1 Sending the kill signal

Any of the commands:

example% kill -9 100 -165
example% kill -s kill 100 -165
example% 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.

Example 2 Avoiding ambiguity with an initial negative number

To avoid an ambiguity of an initial negative number argument specifying either a signal number or a process group, the former is always be the case. Therefore, to send the default signal to a process group (for example, 123), an application should use a command similar to one of the following:

example% kill -TERM -123
example% kill -- -123

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of kill: LANG, LC_ALL , LC_CTYPE, LC_MESSAGES, and NLSPATH.

Exit Status

The following exit values are 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.

Attributes

See attributes(7) for descriptions of the following attributes:

/usr/bin/kill, csh, ksh88, sh

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os
CSI
Enabled
Interface Stability
Committed
Standard

ksh

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os
CSI
Enabled
Interface Stability
Uncommitted

See Also

csh(1), getconf(1), jobs(1), ksh(1), ksh88(1), ps(1), sh(1), shell_builtins(1), wait(1), kill(2), signal(3C), signal.h(3HEAD), attributes(7), environ(7), standards(7)

Notes

/usr/bin/kill

The number of realtime signals supported is defined by the getconf(1) value _POSIX_RTSIG_MAX.

sh

The Bourne shell, sh, has a built-in version of kill to provide the functionality of the kill command for processes identified with a jobid. The sh syntax is:


kill [ -sig ] [ pid ] [ %job ]...
kill -l

csh

The C-shell, csh, also has a built-in kill command, whose syntax is:


kill [-sig][pid][%job]...
kill -l

The csh kill built-in sends the TERM (terminate) signal, by default, or the signal specified, to the specified process ID, the job indicated, or the current job. Signals are either specified by number or by name. There is no default. Typing kill does not send a signal to the current job. If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process is sent a CONT (continue) signal as well.

–l

Lists the signal names that can be sent.

ksh88

The syntax of the ksh88 kill is:


kill [-sig][pid][%job]...
kill -l

The ksh88 kill sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either specified by number or by names (as specified in signal.h(3HEAD) stripped of the SIG prefix). If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process is sent a CONT (continue) signal if it is stopped. The argument job can be the process id of a process that is not a member of one of the active jobs. In the second form, kill –l, the signal numbers and names are listed.

ksh

The syntax of the ksh kill is:


kill [-n signum] [-s signame] job ...
kill [-n signum] [-s signame] -l [arg ...]

With the first form in which –l is not specified, kill sends a signal to one or more processes specified by job. This normally terminates the processes unless the signal is being caught or ignored.

Specify job as one of the following:

number

The process id of job.

-number

The process group id of job.

%number

The job number.

%string

The job whose name begins with string.

%?string

The job whose name contains string.

%+
%%

The current job.

%-

The previous job.

If the signal is not specified with either the –n or the –s option, the SIGTERM signal is used.

If –l is specified, and no arg is specified, then kill writes the list of signals to standard output. Otherwise, arg can be either a signal name, or a number representing either a signal number or exit status for a process that was terminated due to a signal. If a name is specified the corresponding signal number is written to standard output. If a number is specified the corresponding signal name is written to standard output.

–l

List signal names or signal numbers rather than sending signals as described above. The –n and –s options cannot be specified.

–n signum

Specify a signal number to send. Signal numbers are not portable across platforms, except for the following:

0

No signal.

1

HUP

2

INT

3

QUIT

6

ABRT

9

KILL

14

ALRM

15

TERM

–s signame

Specify a signal name to send. The signal names are derived from their names in <signal.h> without the SIG prefix and are case insensitive. kill –l generates the list of signals on the current platform.

kill in ksh exits with one of the following values:

0

At least one matching process was found for each job operand, and the specified signal was successfully sent to at least one matching process.

>0

An error occurred.