kill(2) [redhat man page]
KILL(2) Linux Programmer's Manual KILL(2) NAME
kill - send signal to a process SYNOPSIS
#include <sys/types.h> #include <signal.h> int kill(pid_t pid, int sig); DESCRIPTION
The kill system call can be used to send any signal to any process group or process. If pid is positive, then signal sig is sent to pid. If pid equals 0, then sig is sent to every process in the process group of the current process. If pid equals -1, then sig is sent to every process except for process 1 (init), but see below. If pid is less than -1, then sig is sent to every process in the process group -pid. If sig is 0, then no signal is sent, but error checking is still performed. RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EINVAL An invalid signal was specified. ESRCH The pid or process group does not exist. Note that an existing process might be a zombie, a process which already committed termi- nation, but has not yet been wait()ed for. EPERM The process does not have permission to send the signal to any of the receiving processes. For a process to have permission to send a signal to process pid it must either have root privileges, or the real or effective user ID of the sending process must equal the real or saved set-user-ID of the receiving process. In the case of SIGCONT it suffices when the sending and receiving processes belong to the same session. NOTES
It is impossible to send a signal to task number one, the init process, for which it has not installed a signal handler. This is done to assure the system is not brought down accidentally. POSIX 1003.1-2001 requires that kill(-1,sig) send sig to all processes that the current process may send signals to, except possibly for some implementation-defined system processes. Linux allows a process to signal itself, but on Linux the call kill(-1,sig) does not signal the current process. LINUX HISTORY
Across different kernel versions, Linux has enforced different rules for the permissions required for an unprivileged process to send a signal to another process. In kernels 1.0 to 1.2.2, a signal could be sent if the effective user ID of the sender matched that of the receiver, or the real user ID of the sender matched that of the receiver. From kernel 1.2.3 until 1.3.77, a signal could be sent if the effective user ID of the sender matched either the real or effective user ID of the receiver. The current rules, which conform to POSIX 1003.1-2001, were adopted in kernel 1.3.78. CONFORMING TO
SVr4, SVID, POSIX.1, X/OPEN, BSD 4.3, POSIX 1003.1-2001 SEE ALSO
_exit(2), exit(3), signal(2), signal(7) Linux 2.5.0 2001-12-18 KILL(2)
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kill(2) System Calls kill(2) NAME
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
The kill() function 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 sig- nal.h(3HEAD)), 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 saved (from one of functions in the exec(2) family) user ID of the receiving process, unless the privilege {PRIV_PROC_OWNER} is asserted in the effective set of the sending process (see intro(2)), or sig is SIGCONT and the sending process has the same session ID as the receiving process. A process needs the basic privilege {PRIV_PROC_SESSION} to send signals to a process with a different session ID. See privileges(5). If pid is greater than 0, sig will be sent to the process whose process ID is equal to pid. 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 special processes (see intro(2)) whose process group ID is equal to the process group ID of the sender. If pid is (pid_t)-1 and the {PRIV_PROC_OWNER} privilege is not asserted in the effective set of the sending process, sig will be sent to all processes excluding special processes whose real user ID is equal to the effective user ID of the sender. If pid is (pid_t)-1 and the {PRIV_PROC_OWNER} privilege is asserted in the effective set of the sending process, sig will be sent to all processes excluding special processes. RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is returned, no signal is sent, and errno is set to indicate the error. ERRORS
The kill() function will fail if: EINVAL The sig argument is not a valid signal number. EPERM The sig argument is SIGKILL and the pid argument is (pid_t)-1 (that is, the calling process does not have permission to send the signal to any of the processes specified by pid). The effective user of the calling process does not match the real or saved user and the calling process does not have the {PRIV_PROC_OWNER} privilege asserted in the effective set, and the calling process either is not sending SIGCONT to a process that shares the same session ID or does not have the {PRIV_PROC_SESSION} privilege asserted and is trying to send a signal to a process with a different session ID. ESRCH No process or process group can be found corresponding to that specified by pid. USAGE
The sigsend(2) function provides a more versatile way to send signals to processes. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
kill(1), intro(2), exec(2), getpid(2), getsid(2), setpgrp(2), sigaction(2), sigsend(2), signal(3C), signal.h(3HEAD), attributes(5), privi- leges(5), standards(5) SunOS 5.10 22 Mar 2004 kill(2)