• NAME
  
  kill - send signal to a process
• SYNOPSIS
  

  
   #include <sys/types.h>
  
   #include <signal.h>
  
   int kill(pid_t  pid , int  sig );
  
  
    Feature Test Macro Requirements for glibc (see
  
  
    feature_test_macros(7) ):
  
   
  
      kill ():
  
   _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
  
  
  

• 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 the
  process with the ID specified by pid.
  
  
  
  If pid equals 0, then sig is sent to every process in the
  process group of the calling process.
  
  
  
  If pid equals -1, then sig is sent to every process
  for which the calling process has permission to send signals,
  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 whose ID is -pid.
  
  
  
  If sig is 0, then no signal is sent, but error checking is still
  performed;
  this can be used to check for the existence of a process ID or
  process group ID.
  
  For a process to have permission to send a signal
  it must either be privileged (under Linux: have the
  CAP_KILL capability), or the real or effective
  user ID of the sending process must equal the real or
  saved set-user-ID of the target process.
  In the case of
  SIGCONT it suffices when the sending and receiving
  processes belong to the same session.
  
• RETURN VALUE
  
  On success (at least one signal was sent), zero is returned.
  On error, -1 is returned, and
  errno
  is set appropriately.
  
• ERRORS
  

  EINVAL

  An invalid signal was specified.
  

  EPERM

  The process does not have permission to send the signal
  to any of the target processes.
  

  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(2) ed
  for.
  

• CONFORMING TO
  
  SVr4, 4.3BSD, POSIX.1-2001.
  
• NOTES
  
  The only signals that can be sent to process ID 1, the
  init
  process, are those for which
  init
  has explicitly installed signal handlers.
  This is done to assure the
  system is not brought down accidentally.
  
  POSIX.1-2001 requires that kill(-1,sig) send sig
  to all processes that the calling 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 calling process.
  
  POSIX.1-2001 requires that if a process sends a signal to itself,
  and the sending thread does not have the signal blocked,
  and no other thread
  has it unblocked or is waiting for it in
  sigwait(3) ,
  at least one
  unblocked signal must be delivered to the sending thread before the
  kill ().
  "Linux Notes"
  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.1-2001, were adopted
  in kernel 1.3.78.
  
• BUGS
  
  In 2.6 kernels up to and including 2.6.7,
  there was a bug that meant that when sending signals to a process group,
  kill ()
  failed with the error
  EPERM if the caller did have permission to send the signal to any (rather
  than all) of the members of the process group.
  Notwithstanding this error return, the signal was still delivered
  to all of the processes for which the caller had permission to signal.
  
• SEE ALSO
  
  _exit(2) ,
  killpg(2) ,
  signal(2) ,
  sigqueue(2) ,
  tkill(2) ,
  exit(3) ,
  capabilities(7) ,
  credentials(7) ,
  signal(7)
  
• COLOPHON
  
  This page is part of release 3.19 of the Linux
  man-pages
  project.
  A description of the project,
  and information about reporting bugs,
  can be found at
  http://www.kernel.org/doc/man-pages/.
  

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