tkill(2) System Calls Manual tkill(2)
NAME
tkill, tgkill - send a signal to a thread
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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
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 sig-
nal 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 li-
brary use.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set to indicate the error.
ERRORS
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.
VERSIONS
tkill() is supported since Linux 2.4.19 / 2.5.4. tgkill() was added in
Linux 2.5.75.
Library support for tgkill() was added in glibc 2.30.
STANDARDS
tkill() and tgkill() are Linux-specific and should not be used in pro-
grams that are intended to be portable.
NOTES
See the description of CLONE_THREAD in clone(2) for an explanation of
thread groups.
Before glibc 2.30, there was also no wrapper function for tgkill().
SEE ALSO
clone(2), gettid(2), kill(2), rt_sigqueueinfo(2)
Linux man-pages 6.03 2022-12-04 tkill(2)
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