kill - send signal to process or process group

Syntax

#include <signal.h>

Optional
#include <sys/types.h> (End)

int kill(pid_t pid, int sig);

Description

If the function is called with POSIX functionality, its behavior conforms with XPG4 as described below:

• kill() sends a signal sig to a process or a group of processes specified by pid, where sig is either one from the list given in signal.h or 0. If sig is 0 (the null signal), error checking is performed, but no signal is actually sent. The null signal can be used to check the validity of pid.

• {_POSIX_SAVED_IDS} is defined on all X/Open-conformant systems. For a process to have permission to send a signal to a process designated by pid, the real or effective user ID of the sending process must match the real or saved set-user-ID of the receiving process, unless the sending process has appropriate privileges.

• If pid is greater than 0, sig is sent to the process whose process ID is equal to pid.

• If pid is 0, sig is sent to all processes (excluding a number of system processes) whose process group ID is equal to the process group ID of the sender, and for which the process has permission to send a signal.

• If pid is -1, sig is sent to all processes (excluding system processes) for which the process has permission to send that signal.

• 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, and for which the process has permission to send a signal.

• If the value of pid causes sig to be generated for the sending process, and if sig is not blocked, either sig or at least one pending unblocked signal is delivered to the sending process before kill() returns.

• No user ID test is applied when sending SIGCONT to a process that is a member of the same session as the sending process.

• kill() is successful if the process has permission to send sig to any of the processes specified by pid. If kill() fails, no signal is sent.

If threads are used, then the function affects the process or a thread in the following manner:

• A signal is sent to a process or a process group; The following applies to the (special) case caused by the value of pid in which sig is generated for the sending process: If the signal is not blocked for the calling thread and all other threads of the process block the signal or do not wait for the signal in a sigwait() function, then sig (or at least a follow-up non-blocking signal) is sent to the sending thread before kill() returns.

BS2000

• The following deviations in behavior must be noted if the function is called with BS2000 functionality:

• pid must be 0, so the signal is sent to the calling process.

• The following subset of the signals defined in signal.h can be used for sig:

  Signal	STXIT class	Meaning
  SIGHUP	ABEND	Disconnection of link to terminal
  SIGINT	ESCPBRK	Interrupt from the terminal with [K2]
  SIGILL	PROCHK	Execution of an invalid instruction
  SIGABRT	-	raise signal for program abort with _exit(-1)
  SIGFPE	PROCHK	Error in a floating-point operation
  SIGKILL	-	raise signal for program abort with exit(-1)
  SIGSEGV	ERROR	Memory access with invalid segment access
  SIGALRM	RTIMER	A time interval has elapsed (real time)
  SIGTERM	TERM	Signal at program termination
  SIGUSR1	-	Defined by the user
  SIGUSR2	-	Defined by the user
  SIGDVZ	PROCHK	Division by 0
  SIGXCPU	RUNOUT	CPU time has run out
  SIGTIM	TIMER	A time interval has elapsed (CPU time)
  SIGINTR	INTR	SEND-MESSAGE command

  (End)

Return val.

0

-1

upon successful completion.

if an error occurs. errno is set to indicate the error.

Errors

kill() will fail if: 

 

EINVAL

The value of the sig argument is an invalid or unsupported signal number.

 

EPERM

The process does not have permission to send the signal to any receiving process.

BS2000
EPERM is not supported. (End)

ESRCH

No process or process group can be found corresponding to that specified by pid.

See also

 getpid(), raise(), setsid(), sigaction(), signal.h, sys/types.h.