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.\" Copyright (C) 2008 Michael Kerrisk <tmk.manpages@gmail.com>
.\" and Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
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.\" 2004-05-31, added tgkill, ahu, aeb
.\" 2008-01-15 mtk -- rewote DESCRIPTION
.\"
.TH TKILL 2 2008-01-15 "Linux" "Linux Programmer's Manual"
.SH NAME
tkill, tgkill \- send a signal to a thread
.SH SYNOPSIS
.nf
.BI "int tkill(int " tid ", int " sig );
.sp
.BI "int tgkill(int " tgid ", int " tid ", int " sig );
.fi
.SH DESCRIPTION
.BR tgkill ()
sends the signal
.I sig
to the thread with the thread ID
.I tid
in the thread group
.IR tgid .
(By contrast,
.BR kill (2)
can only be used to send a signal to a process (i.e., thread group)
as a whole, and the signal will be delivered to an arbitrary
thread within that process.)

.BR tkill ()
is an obsolete predecessor to
.BR tgkill ().
It only allows 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
.I tgid
is specified as \-1,
.BR tgkill ()
is equivalent to
.BR tkill ().

These are the raw system call interfaces, meant for internal
thread library use.
.SH "RETURN VALUE"
On success, zero is returned.
On error, \-1 is returned, and \fIerrno\fP
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
An invalid TID or signal was specified.
.TP
.B EPERM
Permission denied.
For the required permissions, see
.BR kill (2).
.TP
.B ESRCH
No process with the specified thread ID (and thread group ID) exists.
.SH VERSIONS
.BR tkill ()
is supported since Linux 2.4.19 / 2.5.4.
.BR tgkill ()
was added in Linux 2.5.75.
.SH "CONFORMING TO"
.BR tkill ()
and
.BR tgkill ()
are Linux-specific and should not be used
in programs that are intended to be portable.
.SH NOTES
See the description of
.B CLONE_THREAD
in
.BR clone (2)
for an explanation of thread groups.

Glibc does not provide wrappers for these system calls; call them using
.BR syscall (2).
.SH "SEE ALSO"
.BR clone (2),
.BR gettid (2),
.BR gettid (2),
.BR kill (2)