table of contents
|KILL(2)||System Calls Manual||KILL(2)|
kill — send signal
to a process
Standard C Library (libc, -lc)
pid, int sig);
system call sends the signal given by sig to
pid, a process or a group of processes. The
sig argument may be one of the signals specified in
sigaction(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.
For a process to have permission to send a signal to a process designated by pid, the user must be the super-user, or the real or saved user ID of the receiving process must match the real or effective user ID of the sending process. A single exception is the signal SIGCONT, which may always be sent to any process with the same session ID as the sender. In addition, if the security.bsd.conservative_signals sysctl(9) is set to 1, the user is not a super-user, and the receiver is set-uid, then only job control and terminal control signals may be sent (in particular, only SIGKILL, SIGINT, SIGTERM, SIGALRM, SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2).
- If pid is greater than zero:
- The sig signal is sent to the process whose ID is equal to pid.
- If pid is zero:
- The sig signal is sent to all processes whose group ID is equal to the process group ID of the sender, and for which the process has permission; this is a variant of killpg(2).
- If pid is -1:
- If the user has super-user privileges, the signal is sent to all processes
excluding system processes (with
P_SYSTEMflag set), process with ID 1 (usually init(8)), and the process sending the signal. If the user is not the super user, the signal is sent to all processes which the caller has permissions to, excluding the process sending the signal. No error is returned if any process could be signaled.
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).
kill() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
kill() system call will fail and no
signal will be sent if:
getpgrp(2), getpid(2), killpg(2), sigaction(2), sigqueue(2), raise(3), init(8)
kill() system call is expected to
conform to IEEE Std 1003.1-1990
A version of the
kill() function appeared
in Version 3 AT&T UNIX. The signal number
was added to the
kill() function in
Version 4 AT&T UNIX.
|December 1, 2019||Debian|