tkill, tgkill - send a signal to a thread


int tkill(int tid, int sig);

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


tgkill() sends the signal sig to the thread with the thread ID tid in the thread group tgid. (By contrast, 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.)

tkill() is an obsolete predecessor to 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 tgid is specified as -1, tgkill() is equivalent to tkill().

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


On success, zero is returned. On error, -1 is returned, and errno is set appropriately.


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.


tkill() is supported since Linux 2.4.19 / 2.5.4. tgkill() was added in Linux 2.5.75.


tkill() and tgkill() are Linux-specific and should not be used in programs that are intended to be portable.


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).


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


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