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CentOS 7.0 - man page for tkill (centos section 2)

TKILL(2)						     Linux Programmer's Manual							  TKILL(2)

NAME
tkill, tgkill - send a signal to a thread
SYNOPSIS
int tkill(int tid, int sig); int tgkill(int tgid, int tid, int sig); Note: There are no glibc wrappers for these system calls; see NOTES.
DESCRIPTION
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. If tgid is specified as -1, tgkill() is equivalent to tkill(). These are the raw system call interfaces, meant for internal thread library use.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
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.
VERSIONS
tkill() is supported since Linux 2.4.19 / 2.5.4. tgkill() was added in Linux 2.5.75.
CONFORMING TO
tkill() and tgkill() are Linux-specific and should not be used in programs that are intended to be portable.
NOTES
See the description of CLONE_THREAD in clone(2) for an explanation of thread groups. Glibc does not provide wrappers for these system calls; call them using syscall(2).
SEE ALSO
clone(2), gettid(2), kill(2), rt_sigqueueinfo(2)
COLOPHON
This page is part of release 3.53 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/. Linux 2012-07-13 TKILL(2)