kill

Sends a signal to a process or a process group.

Syntax

   #include <sys/types.h>

   #include <signal.h>

   int kill (pid_t pid, int sig);

Parameters

pid

A value indicating the process or process group to receive the signal specified in sig. Following are valid values and their meanings:

>0: A process whose process ID is equal to pid.
0: All processes whose process group ID is equal to the caller's process group ID.
<-1: All processes whose process group ID is equal to the absolute value of pid.

If -1 is passed in pid, kill() fails and sets errno to EINVAL.

sig

A value indicating the signal to be sent. Following are valid values and their meanings:

>0: The signal number of the signal to send. Refer to Table 3-6 “POSIX/iX Signals” for a list of supported signals and their symbolic constants.
0: Test for existence of specified process or process group. (0 is equivalent to the null signal.)

Return Values

0: Success. The kill() function had permission to send the signal to at least one of the processes specified in pid.
-1: An error occurred. No signal is sent, and errno is set to indicate the error condition.

Description

The kill() function sends a signal specified by sig to a process or group of processes specified by pid. If sig is 0 (the null signal), no signal is sent, but error checking is performed. Use the null signal to check for the validity of pid.

The signal is sent only if the caller has permission to send it to the target process(es). The calling process has permission to send a signal to a target process if one of the following conditions is true:

The user associated with the calling process has appropriate privileges, defined to be one of the following:
- A user whose GID matches the GID of the file and who has the MPE/iX account manager (AM) user capability.
- A user who has the MPE/iX system manager (SM) user capability.
The signal is SIGCONT and the caller's session ID matches the target's session ID.
The caller's real UID matches either the target's real UID or its saved set-user-ID.
The caller's effective UID matches either the target's real user ID or its saved set-user-ID.
The target's UID has been modified by a call to one of the exec() functions.

A target process that is blocking a signal does not receive that signal until it unblocks it. (Refer to the sigaction() function.) A target process can ignore a signal or install a handler for it. The calling process should not assume that the target process will take the default (or any other) action for the signal.

If the value of pid causes sig to be generated for the calling process, and if sig is not blocked, either sig or at least one pending and unblocked signal is delivered to the calling process before the kill() function returns.

Implementation Considerations

Job control is not supported.

The {POSIX_SAVED_IDS} constant is always defined.

Use the kill() function to send SIGCONT to a process to continue it after SIGSTOP has stopped it. The system never generates SIGCONT and SIGSTOP for a process.

A sending process cannot rely on the target process acting upon a signal in a timely manner if the target process is executing operating system code. The target process is not interrupted until it returns from operating system code.

Refer to Table 3-6 “POSIX/iX Signals” for implementation considerations associated with signals.

Errors

If an error occurs, errno is set to one of the following values:

`EINVAL`	CAUSE	The signal `sig` is not a valid signal number, or `pid` is -1.
	ACTION	Refer to Table 3-6 “POSIX/iX Signals” for descriptions of valid signal numbers, or set `pid` to a valid value.
`EPERM`	CAUSE	One of the following: The calling process does not have the MPE/iX process handling (PH) capability. The calling process has outstanding switches to CM code, has set critical mode, has outstanding NOWAITIO, or is holding an operating system internal resource, or the calling process is in a Procedure Exit handler.
	ACTION	One of the following: Link the program file with the MPE/iX PH capability. Do not execute `execl()` when the calling process has outstanding switches to CM code, has set critical mode, has outstanding NOWAITIO, or is holding an operating system internal resource, or in a Procedure Exit handler.
`ESRCH`	CAUSE	No process or process group matches `pid`.
	ACTION	No action required.

kill

Technical documentation

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