The kill
function can be used to send a signal to another process.
In spite of its name, it can be used for a lot of things other than
causing a process to terminate. Some examples of situations where you
might want to send signals between processes are:
This section assumes that you know a little bit about how processes work. For more information on this subject, see section Processes.
The kill
function is declared in `signal.h'.
kill
function sends the signal signum to the process
or process group specified by pid. Besides the signals listed in
section Standard Signals, signum can also have a value of zero to
check the validity of the pid.
The pid specifies the process or process group to receive the signal:
pid > 0
pid == 0
pid < -1
pid == -1
A process can send a signal to itself with a call like kill
(getpid(), signum)
. If kill
is used by a process to send
a signal to itself, and the signal is not blocked, then kill
delivers at least one signal (which might be some other pending
unblocked signal instead of the signal signum) to that process
before it returns.
The return value from kill
is zero if the signal can be sent
successfully. Otherwise, no signal is sent, and a value of -1
is
returned. If pid specifies sending a signal to several processes,
kill
succeeds if it can send the signal to at least one of them.
There's no way you can tell which of the processes got the signal
or whether all of them did.
The following errno
error conditions are defined for this function:
EINVAL
EPERM
ESCRH
kill
, but sends signal signum to the
process group pgid. This function is provided for compatibility
with BSD; using kill
to do this is more portable.
As a simple example of kill
, the call kill (getpid (),
sig)
has the same effect as raise (sig)
.
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