int kill(pid_t pid, int sig);
The specification for "kill" is as specified in the SUSv2 but with the following differences as listed below.
If pid is specified as -1, sig shall not be sent to the calling process. Other than this, the rules in the SUSv2 apply.
This was a deliberate Linus decision after an unpopular experiment in including the calling process in the 2.5.1 kernel. See "What does it mean to signal everybody?", Linux Weekly News, 20 December 2001, http://lwn.net/2001/1220/kernel.php3