tkill(2) — Linux manual page

tkill(2)                   System Calls Manual                   tkill(2)

NAME         top

       tkill, tgkill - send a signal to a thread

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <signal.h>           /* Definition of SIG* constants */
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       [[deprecated]] int syscall(SYS_tkill, pid_t tid, int sig);

       #include <signal.h>

       int tgkill(pid_t tgid, pid_t tid, int sig);

       Note: glibc provides no wrapper for tkill(), necessitating the use
       of syscall(2).

DESCRIPTION         top

       tgkill() sends the signal sig to the thread with the thread ID tid
       in the thread group tgid.  (By contrast, kill(2) can be used to
       send a signal only to a process (i.e., thread group) as a whole,
       and the signal will be delivered to an arbitrary thread within
       that process.)

       tkill() is an obsolete predecessor to tgkill().  It allows only
       the target thread ID to be specified, which may result in the
       wrong thread being signaled if a thread terminates and its thread
       ID is recycled.  Avoid using this system call.

       These are the raw system call interfaces, meant for internal
       thread library use.

RETURN VALUE         top

       On success, zero is returned.  On error, -1 is returned, and errno
       is set to indicate the error.

ERRORS         top

       EAGAIN The RLIMIT_SIGPENDING resource limit was reached and sig is
              a real-time signal.

       EAGAIN Insufficient kernel memory was available and sig is a real-
              time signal.

       EINVAL An invalid thread ID, thread group ID, or signal was
              specified.

       EPERM  Permission denied.  For the required permissions, see
              kill(2).

       ESRCH  No process with the specified thread ID (and thread group
              ID) exists.

STANDARDS         top

       Linux.

HISTORY         top

       tkill()
              Linux 2.4.19 / 2.5.4.

       tgkill()
              Linux 2.5.75, glibc 2.30.

NOTES         top

       See the description of CLONE_THREAD in clone(2) for an explanation
       of thread groups.

SEE ALSO         top

       clone(2), gettid(2), kill(2), rt_sigqueueinfo(2)

COLOPHON         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
       This page was obtained from the tarball man-pages-6.15.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2025-08-11.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.15            2025-05-17                       tkill(2)

Pages that refer to this page: clone(2),  gettid(2),  kill(2),  ptrace(2),  rt_sigqueueinfo(2),  sigaction(2),  syscalls(2),  raise(3),  nptl(7),  signal(7)

HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.