kill - send signal to a process
int kill(pid_t pid, int sig);
The kill(2) system call can be used to send any signal to any process group or process.
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 except for the first one.
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. This is an excellent way to see if a process is still running, send it signal 0, then check to see if you got ESRCH as an error.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- An invalid signal was specified.
- 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 wait4(2)ed for.
- The process does not have permission to send the signal to any of the receiving processes. For a process to have permission to send a signal to process pid it must either have root privileges, or the real or effective user ID of the sending process must equal the real or saved set-user-ID of the receiving process. In the case of SIGCONT it suffices when the sending and receiving processes belong to the same session.
It is impossible to send a signal to task number one, the init process, for which it has not installed a signal handler. This is done to assure the system is not brought
SVr4, SVID, POSIX.1, X/OPEN, BSD 4.3
_exit(2), exit(3), signal(2), signal(7)