SIGVEC(3) | Library Functions Manual | SIGVEC(3)

# NAME

`sigvec` — software signal facilities

# SYNOPSIS

`#include <signal.h>`

    struct sigvec {
    	void	 (*sv_handler)();
    	int	 sv_mask;
    	int      sv_flags;
    };

int
`sigvec`(int sig, struct sigvec *vec, struct sigvec *ovec);

# DESCRIPTION

This interface is made obsolete by sigaction(2).

The system defines a set of signals that may be delivered to a process. Signal delivery resembles the occurrence of a hardware interrupt: the signal is blocked from further occurrence, the current process context is saved, and a new one is built. A process may specify a handler to which a signal is delivered, or specify that a signal is to be blocked or ignored. A process may also specify that a default action is to be taken by the system when a signal occurs. A signal may also be blocked, in which case its delivery is postponed until it is unblocked. The action to be taken on delivery is determined at the time of delivery. Normally, signal handlers execute on the current stack of the process. This may be changed, on a per-handler basis, so that signals are taken on a special signal stack.

All signals have the same priority. Signal routines execute with the signal that caused their invocation blocked, but other signals may yet occur. A global signal mask defines the set of signals currently blocked from delivery to a process. The signal mask for a process is initialized from that of its parent (normally 0). It may be changed with a sigblock(3) or sigsetmask(3) call, or when a signal is delivered to the process.

When a signal condition arises for a process, the signal is added to a set of signals pending for the process. If the signal is not currently blocked by the process then it is delivered to the process. When a caught signal is delivered, the current state of the process is saved, a new signal mask is calculated (as described below), and the signal handler is invoked. The call to the handler is arranged so that if the signal handling routine returns normally the process will resume execution in the context from before the signal's delivery. If the process wishes to resume in a different context, then it must arrange to restore the previous context itself.

When a signal is delivered to a process, a new signal mask is installed for the duration of the process' signal handler (or until a sigblock(3) or sigsetmask(3) call is made). This mask is formed by taking the union of the current signal mask, the signal to be delivered, and the signal mask associated with the handler to be invoked.

`sigvec`() assigns a handler for a specific signal. If vec is non-zero, it specifies an action (`SIG_DFL`, `SIG_IGN`, or a handler routine) and mask to be used when delivering the specified signal. If ovec is non-zero, the previous handling information for the signal is returned to the user.

Once a signal handler is installed, it remains installed until another `sigvec`() call is made, or an execve(2) is performed. A signal-specific default action may be reset by setting sv_handler to `SIG_DFL`. The defaults are process termination, possibly with core dump; no action; stopping the process; or continuing the process. See the signal list below for each signal's default action. If sv_handler is set to `SIG_IGN`, the default action for the signal is to discard the signal, and if a signal is pending, the pending signal is discarded even if the signal is masked. If sv_handler is set to `SIG_IGN`, current and pending instances of the signal are ignored and discarded.

Options may be specified by setting sv_flags. If the `SV_ONSTACK` bit is set in sv_flags, the system will deliver the signal to the process on a signal stack, specified with sigaltstack(2).

If a signal is caught during the system calls listed below, the call may be restarted, the call may return with a data transfer shorter than requested, or the call may be forced to terminate with the error `EINTR`. Interrupting of pending calls is requested by setting the `SV_INTERRUPT` bit in sv_flags. The affected system calls include open(2), read(2), write(2), sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications channel or a slow device (such as a terminal, but not a regular file) and during a wait(2) or ioctl(2). However, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count).

After a fork(2) or vfork(2) all signals, the signal mask, the signal stack, and the interrupt/restart flags are inherited by the child.

execve(2) reinstates the default action for all signals which were caught and resets all signals to be caught on the user stack. Ignored signals remain ignored; the signal mask remains the same; signals that interrupt pending system calls continue to do so.

The following is a list of all signals with names as in the include file `<signal.h>`:

Name | Default Action | Description
`SIGHUP` | terminate process | terminal line hangup
`SIGINT` | terminate process | interrupt program
`SIGQUIT` | create core image | quit program
`SIGILL` | create core image | illegal instruction
`SIGTRAP` | create core image | trace trap
`SIGABRT` | create core image | abort(3) call (formerly SIGIOT)
`SIGEMT` | create core image | emulate instruction executed
`SIGFPE` | create core image | floating-point exception
`SIGKILL` | terminate process | kill program (cannot be caught or ignored)
`SIGBUS` | create core image | bus error
`SIGSEGV` | create core image | segmentation violation
`SIGSYS` | create core image | system call given invalid argument
`SIGPIPE` | terminate process | write on a pipe with no reader
`SIGALRM` | terminate process | real-time timer expired
`SIGTERM` | terminate process | software termination signal
`SIGURG` | discard signal | urgent condition present on socket
`SIGSTOP` | stop process | stop (cannot be caught or ignored)
`SIGTSTP` | stop process | stop signal generated from keyboard
`SIGCONT` | discard signal | continue after stop
`SIGCHLD` | discard signal | child status has changed
`SIGTTIN` | stop process | background read attempted from controlling terminal
`SIGTTOU` | stop process | background write attempted to controlling terminal
`SIGIO` | discard signal | I/O is possible on a descriptor (see fcntl(2))
`SIGXCPU` | terminate process | CPU time limit exceeded (see setrlimit(2))
`SIGXFSZ` | terminate process | file size limit exceeded (see setrlimit(2))
`SIGVTALRM` | terminate process | virtual time alarm (see setitimer(2))
`SIGPROF` | terminate process | profiling timer alarm (see setitimer(2))
`SIGWINCH` | discard signal | window size change
`SIGINFO` | discard signal | status request from keyboard
`SIGUSR1` | terminate process | user-defined signal 1
`SIGUSR2` | terminate process | user-defined signal 2

# NOTES

The mask specified in vec is not allowed to block `SIGKILL` or `SIGSTOP`. This is enforced silently by the system.

The `SV_INTERRUPT` flag is not available in 4.2BSD, hence it should not be used if backward compatibility is needed.

# RETURN VALUES

A 0 value indicated that the call succeeded. A -1 return value indicates an error occurred and errno is set to indicated the reason.

# EXAMPLES

For an example of signal handler declarations, see sigaction(2).

# ERRORS

`sigvec`() will fail and no new signal handler will be installed if one of the following occurs:

[`EFAULT`]
  Either vec or ovec points to memory that is not a valid part of the process address space.
[`EINVAL`]
  sig is not a valid signal number.
[`EINVAL`]
  An attempt is made to ignore or supply a handler for `SIGKILL` or `SIGSTOP`.

# SEE ALSO

kill(1), kill(2), ptrace(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsuspend(2), setjmp(3), sigaddset(3), sigblock(3), siginterrupt(3), sigpause(3), sigsetmask(3), tty(4)

# HISTORY

A `sigvec`() system call first appeared in 4.2BSD. It was reimplemented as a wrapper around sigaction(2) in 4.3BSD-Reno. The old system call was kept for compatibility until OpenBSD 4.9.

October 13, 2022 | Debian