kill(S)
kill --
send a signal to a process or a group of processes
Synopsis
#include <sys/types.h>
#include <signal.h>
int kill(pid_t pid, int 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
[see
signal(M)],
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.
In order to send the signal to the target process (pid),
the sending process must have permission to do so, subject to the
following ownership restrictions:
-
The real or effective user ID of the sending process must match
the real or saved [from exec] user ID of the receiving process,
unless the sending process has the P_OWNER privilege, or
sig is SIGCONT and the sending process has the same session
ID as the receiving process.
The process with ID 0 and the process with ID
1 are special processes [see
intro(S)]
and will be referred to below as proc0 and proc1, respectively.
If pid is greater than 0, sig
will be sent to the process whose process ID
is equal to pid,
subject to the ownership restrictions, above.
pid
may equal 1.
If
pid
is negative but not (pid_t)-1,
sig will be sent to all processes whose process group
ID is equal to the absolute value of
pid
and for which the process has permission to send a signal.
If
pid
is 0,
sig
will be sent to all processes excluding proc0 and proc1
whose process group ID is equal to the process group
ID of the sender.
Permission is needed to send a signal to process groups.
If pid is (pid_t)-1 and
the sending process does not have the P_OWNER privilege,
sig will be 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 (pid_t)-1 and
the sending process has the P_OWNER privilege,
sig
will be sent to all processes excluding proc0 and proc1.
Return values
On success, kill returns 0.
On failure, kill returns -1, sets errno to identify the error,
and sends no signal.
Errors
In the following conditions, kill fails and sets errno to:
EINVAL-
sig is not a valid signal number.
EPERM-
sig is SIGKILL and pid is (pid_t)1
(i.e., pid specifies proc1).
EPERM-
The sending process does not have the P_OWNER privilege,
the real or effective user ID of the sending process
does not match the real or saved user ID
of the receiving process, and the calling process is
not sending SIGCONT to a process that shares the same session ID.
ESRCH-
No process or process group can be found corresponding to that specified
by pid.
Also see ``Standards conformance'', below.
Standards conformance
The default behavior of kill conforms to X/Open System Headers
and Interfaces, Volume 4, Issue 2.
The default behavior of kill is to fail with ESRCH if
a process table entry is found matching pid, but that process
is a zombie (a process that has exited, but whose entries have not yet
been removed from system tables).
Federal Information Processing Standard (FIPS) 151-2 requires
that kill applied to a zombie process (or to a set of processes
all of which are zombies) to succeed instead of failing with ESRCH.
To get this behavior, change the PROCSET_ZOMBIES system tunable
from ``0'' (the default value) to ``1'' and rebuild the kernel.
References
getpid(S),
getsid(S),
intro(S),
kill(C),
setpgrp(S),
sigaction(S),
signal(S),
sigsend(S)
Notices
sigsend is a more versatile way to send signals to processes.
The user is encouraged to use sigsend instead of kill.
Considerations for threads programming
Signals can be posted from one process to another via kill
but not to specific threads within the receiving process.
See
signal(M)
for further details.
See
thr_kill(THREAD)
for intra-process, thread-to-thread signaling.
Considerations for lightweight processes
Additionally, signals from one process cannot be addressed to specific
LWPs in the receiving process.
© 2005 The SCO Group, Inc. All rights reserved.
SCO OpenServer Release 6.0.0 - 01 June 2005