NAME

kill − send a signal to a process or a group of processes

SYNOPSIS

int kill (pid, sig)
int pid, sig;

DESCRIPTION

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 or effective user ID of the receiving process, unless the effective user ID of the sending process is super-user. 

The processes with a process ID of 0 and a process ID of 1 are special processes [see intro(2)] and are referred to below as proc0 and proc1, respectively.

If pid is greater than zero, sig is sent to the process whose process ID is equal to pid. Pid may equal 1. 

If pid is 0, sig is 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 is 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 is sent to all processes excluding proc0 and proc1. 

If pid is negative but not −1, sig is sent to all processes whose process group ID is equal to the absolute value of pid.

kill fails and no signal is sent if one or more of the following are true:

Sending a signal to a multi-threaded process causes the signal to be sent to one and only one of the threads. 

­[EINVAL]
sig is not a valid signal number. 

­[EINVAL] sig is SIGKILL and pid is 1 (proc1). 

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

­[EPERM] The user ID of the sending process is not super-user, and its real or effective user ID does not match the real or effective user ID of the receiving process. 

SEE ALSO

getpid(2), kill(1), setpgrp(2), signal(2), sigset(2), thread(2). 

DIAGNOSTICS

Upon successful completion, a value of 0 is returned.  Otherwise, a value of −1 is returned and errno is set to indicate the error. 

September 02, 1992