NAME

       kill — send signal to a process

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <sys/types.h>
       #include <signal.h>

       int
       kill(pid_t pid, int sig);

DESCRIPTION

       The  kill() 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_SYSTEM flag 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).

RETURN VALUES

       The kill() function returns the value 0 if successful; otherwise the value -1 is returned and the  global
       variable errno is set to indicate the error.

ERRORS

       The kill() system call will fail and no signal will be sent if:

       [EINVAL]           The sig argument is not a valid signal number.

       [ESRCH]            No process or process group can be found corresponding to that specified by pid.

       [EPERM]            The sending process does not have permission to send sig to any receiving process.

SEE ALSO

       getpgrp(2), getpid(2), killpg(2), sigaction(2), sigqueue(2), raise(3), init(8)

STANDARDS

       The kill() system call is expected to conform to ISO/IEC 9945-1:1990 (“POSIX.1”).

HISTORY

       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.

Debian                                          December 1, 2019                                         KILL(2)