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KILL   (2) manpage
KILL
2
2001-12-18
Linux 2.5.0
Linux Programmer's Manual
  • 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 termination, 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
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