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 sig-
nal 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 tar-
get thread ID to be specified, which may result in the wrong thread be-
ing 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) ex-
ists.
STANDARDS
Linux.
HISTORY
tkill()
Linux 2.4.19 / 2.5.4.
tgkill()
Linux 2.5.75, glibc 2.30.
NOTES
See the description of CLONE_THREAD in clone(2) for an explanation of
thread groups.
SEE ALSO
clone(2), gettid(2), kill(2), rt_sigqueueinfo(2)
Linux man-pages 6.9.1 2024-05-02 tkill(2)
Generated by dwww version 1.16 on Tue Dec 16 04:02:03 CET 2025.