kill - 發送信號給一個進程

內容簡介

#include <sys/types.h>
#include <signal.h>

int kill(pid_t pid**, int** sig**);**

描述

kill () 系統調用可以用來發送任何信號，任何進程組或進程。

If pid is positive, then signal sig is sent to pid.

If pid equals 0, then sig is sent to every process in the process group of the current process.

If pid equals -1, then sig is sent to every process for which the calling process has permission to send signals, except for process 1 (init), but see below.

If pid is less than -1, then sig is sent to every process in the process group -pid.

If sig is 0, then no signal is sent, but error checking is still performed.

For a process to have permission to send a signal it must either be privileged (under Linux: have the CAP_KILL capability), or the real or effective user ID of the sending process must equal the real or saved set-user-ID of the target process. In the case of SIGCONT it suffices when the sending and receiving processes belong to the same session.

返回值

On success (at least one signal was sent), zero is returned. On error, -1 is returned, and  errno  is set appropriately.

錯誤

標籤

描述

EINVAL

An invalid signal was specified.

EPERM

The process does not have permission to send the signal to any of the target processes.

ESRCH

The pid or process group does not exist. Note that an existing process might be a zombie, a process which already committed termination, but has not yet been wait()ed for.

注意

可發送任務一把手，init進程的唯一信號，是那些已經初始化安裝了​​明確的信號處理程序。這樣做是爲了保證系統不放倒意外。

POSIX.1-2001 requires that kill(-1,sig) send sig to all processes that the current process may send signals to, except possibly for some implementation-defined system processes. Linux allows a process to signal itself, but on Linux the call kill(-1,sig) does not signal the current process.

POSIX.1-2001 requires that if a process sends a signal to itself, and the sending thread does not have the signal blocked, and no other thread has it unblocked or is waiting for it in sigwait(), at least one unblocked signal must be delivered to the sending thread before the kill().

BUGS

In 2.6 kernels up to and including 2.6.7, there was a bug that meant that when sending signals to a process group,  kill () failed with the error  EPERM  if the caller did have permission to send the signal to  any  (rather than  all ) of the members of the process group. Notwithstanding this error return, the signal was still delivered to all of the processes for which the caller had permission to signal.

LINUX HISTORY

Across different kernel versions, Linux has enforced different rules for the permissions required for an unprivileged process to send a signal to another process. In kernels 1.0 to 1.2.2, a signal could be sent if the effective user ID of the sender matched that of the receiver, or the real user ID of the sender matched that of the receiver. From kernel 1.2.3 until 1.3.77, a signal could be sent if the effective user ID of the sender matched either the real or effective user ID of the receiver. The current rules, which conform to POSIX.1-2001, were adopted in kernel 1.3.78.

遵循於

SVr4, 4.3BSD, POSIX.1-2001

另請參閱

• _exit (2)

• killpg (2)

• signal (2)

• sigqueue (2)

• tkill (2)