KILL(2) BSD System Calls Manual KILL(2)
kill -- send signal to a process
Standard C Library (libc, -lc)
kill(pid_t pid, int sig);
The kill() function sends the signal given by sig to pid, a process or a group of processes.
sig 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 valid-
ity of pid.
For a process to have permission to send a signal to a process designated by pid, the real
or effective user ID of the receiving process must match that of the sending process or the
user must have appropriate privileges (such as given by a set-user-ID program or the user is
the super-user). A single exception is the signal SIGCONT, which may always be sent to any
descendant of the current process.
If pid is greater than zero:
sig is sent to the process whose ID is equal to pid.
If pid is zero:
sig is sent to all processes whose process group ID is equal to the process group ID
of the sender, and for which the process has permission; this is a variant of
If pid is -1:
If the user has super-user privileges, the signal is sent to all processes excluding
system processes 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 sig-
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(3).
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned
and errno is set to indicate the error.
kill() will fail and no signal will be sent if:
[EINVAL] sig is not a valid signal number.
[ESRCH] No process can be found corresponding to that specified by pid.
[ESRCH] The process id was given as 0 but the sending process does not have a
[EPERM] The sending process is not the super-user and its effective user id does
not match the effective user-id of the receiving process. When signaling
a process group, this error is returned if any members of the group could
not be signaled.
getpgrp(2), getpid(2), sigaction(2), killpg(3), signal(7)
The kill() function is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1'').
BSD April 19, 1994 BSD