These functions provide simplified signal management for application processes. See signal(3HEAD) for an explanation of general signal concepts.

The signal() and sigset() functions modify signal dispositions. The sig argument specifies the signal, which may be any signal except SIGKILL and SIGSTOP. The disp argument specifies the signal's disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal handler. If signal() is used, disp is the address of a signal handler, and sig is not SIGILL, SIGTRAP, or SIGPWR, the system first sets the signal's disposition to SIG_DFL before executing the signal handler. If sigset() is used and disp is the address of a signal handler, the system adds sig to the calling process's signal mask before executing the signal handler; when the signal handler returns, the system restores the calling process's signal mask to its state prior to the delivery of the signal. In addition, if sigset() is used and disp is equal to SIG_HOLD, sig is added to the calling process's signal mask and the signal's disposition remains unchanged.

The sighold() function adds sig to the calling process's signal mask.

The sigrelse() function removes sig from the calling process's signal mask.

The sigignore() function sets the disposition of sig to SIG_IGN.

The sigpause() function removes sig from the calling process's signal mask and suspends the calling process until a signal is received.

Upon successful completion, signal() returns the signal's previous disposition. Otherwise, it returns SIG_ERR and sets errno to indicate the error.

Upon successful completion, sigset() returns SIG_HOLD if the signal had been blocked or the signal's previous disposition if it had not been blocked. Otherwise, it returns SIG_ERR and sets errno to indicate the error.

Upon successful completion, sighold(), sigrelse(), sigignore(), and sigpause(), return 0. Otherwise, they return -1 and set errno to indicate the error.

These functions fail if:

EINTR

A signal was caught during the execution sigpause().

EINVAL

The value of the sig argument is not a valid signal or is equal to SIGKILL or SIGSTOP.

The sighold() function used in conjunction with sigrelse() or sigpause() may be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

If signal() or sigset() is used to set SIGCHLD's disposition to a signal handler, SIGCHLD will not be sent when the calling process's children are stopped or continued.

If any of the above functions are used to set SIGCHLD's disposition to SIG_IGN, the calling process's child processes will not create zombie processes when they terminate (see exit(2)). If the calling process subsequently waits for its children, it blocks until all of its children terminate; it then returns -1 with errno set to ECHILD (see wait(2) and waitid(2)).

The system guarantees that if more than one instance of the same signal is generated to a process, at least one signal will be received. It does not guarantee the reception of every generated signal.

See attributes(5) for descriptions of the following attributes:

exit(2), kill(2), pause(2), sigaction(2), sigsend(2), wait(2), waitid(2), signal(3HEAD), attributes(5)