KILL(2) System Calls Manual KILL(2)
kill - send signal to a process
int pid, sig;
Kill sends the signal sig to a process, specified by the process number pid. Sig may be one of the signals specified in sigvec(2), or it
may be 0, in which case error checking is performed but no signal is actually sent. This can be used to check the validity of pid.
The sending and receiving processes must have the same effective user ID, otherwise this call is restricted to the super-user. A single
exception is the signal SIGCONT, which may always be sent to any descendant of the current process.
If the process number is 0, the signal is sent to all processes in the sender's process group; this is a variant of killpg(2).
If the process number is -1 and the user is the super-user, the signal is broadcast universally except to system processes and the process
sending the signal. If the process number is -1 and the user is not the super-user, the signal is broadcast universally to all processes
with the same uid as the user except the process sending the signal. No error is returned if any process could be signaled.
For compatibility with System V, if the process number is negative but not -1, the signal is sent to all processes whose process group ID
is equal to the absolute value of the process number. This is a variant of killpg(2).
Processes may send signals to themselves.
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
Kill will fail and no signal will be sent if any of the following occur:
[EINVAL] Sig is not a valid signal number.
[ESRCH] No process can be found corresponding to that specified by pid.
[ESRCH] The process id was given as 0 but the sending process does not have a process group.
[EPERM] The sending process is not the super-user and its effective user id does not match the effective user-id of the receiving
process. When signaling a process group, this error was returned if any members of the group could not be signaled.
getpid(2), getpgrp(2), killpg(2), sigvec(2)
4th Berkeley Distribution May 14, 1986 KILL(2)