SYNOPSISIn sys/types.h In signal.h Ft int Fn kill pid_t pid int sig
DESCRIPTIONThe Fn kill system call sends the signal given by Fa sig to Fa pid , a process or a group of processes. The Fa 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 Fa pid .
For a process to have permission to send a signal to a process designated by Fa 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 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 Fa pid is greater than zero
- The Fa sig signal is sent to the process whose ID is equal to Fa pid .
- If Fa pid is zero
- The Fa 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 Fa 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 with the same uid as the user excluding 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).
RETURN VALUESRv -std kill
ERRORSThe Fn kill system call will fail and no signal will be sent if:
- Bq Er EINVAL
- The Fa sig argument is not a valid signal number.
- Bq Er ESRCH
- No process or process group can be found corresponding to that specified by Fa pid .
- Bq Er EPERM
- The sending process does not have permission to send sig to the receiving process.
STANDARDSThe Fn kill system call is expected to conform to St -p1003.1-90 .
HISTORYThe Fn kill function appeared in AT&T System v7 .