kill - send a signal to a process or a group of processes
int kill (pid_t pid, int sig);
kill sends a signal to a process or a group of processes. The process or
group of processes to which the signal is to be sent is specified by pid.
The signal that is to be sent is specified by sig and is either one from
the list given in signal(2), or 0. If sig is 0 (the null signal), error
checking is performed but no signal is actually sent. This can be used
to check the validity of pid.
The real or effective user ID of the sending process must match the real,
saved, or effective user ID of the receiving process, unless the
effective user ID of the sending process is super-user. An exception to
this is the signal SIGCONT, which may be sent to any descendant, or any
process in the same session (having the same session ID) as the current
The processes with a process ID of 0 and a process ID of 1 are special
processes [see intro(2)] and will be referred to below as proc0 and
If pid is greater than zero, sig will be sent to the process whose
process ID is equal to pid. Pid may equal 1.
If pid is 0, sig will be sent to all processes excluding proc0 and proc1
whose process group ID is equal to the process group ID of the sender.
If pid is -1 and the effective user ID of the sender is not super-user,
sig will be sent to all processes excluding proc0 and proc1 whose real
user ID is equal to the effective user ID of the sender.
If pid is -1 and the effective user ID of the sender is super-user, sig
will be sent to all processes excluding proc0 and proc1.
If pid is negative but not -1, sig will be sent to all processes whose
process group ID is equal to the absolute value of pid.
If the value of pid causes sig to be generated for the sending process,
and if sig is not blocked for the calling thread and if no other thread
has sig unblocked or is waiting in a sigwait function for sig, either sig
or at least one pending unblocked signal shall be delivered to the
calling thread before the kill() function returns.
kill will fail and no signal will be sent if one or more of the following
[EINVAL] Sig is not a valid signal number.
[EPERM] Sig is SIGKILL and pid is 1 (proc1).
[ESRCH] No process can be found corresponding to that specified by
[ESRCH] The process group was given as 0 but the sending process
does not have a process group.
[EPERM] The user ID of the sending process is not super-user, and
its real or effective user ID does not match the real,
saved, or effective user ID of the receiving process.
kill(1), exec(2), getpid(2), setpgrp(2), setsid(2), signal(2), sigset(2),
sigaction(2), sigprocmask(2), sigqueue(3), sigwait(3), sigvec(3B),
sigblock(3B), sigsetmask(3B), killpg(3B), pthread_kill(3P)
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
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