--- name: "sigvec" section: "2" platform: "macos" package: "Libc" version: "1752.120.2" release: "macOS 26.5" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/sigvec" --- # sigvec(2) software signal facilities ## NAME **sigvec** – software signal facilities ## LIBRARY Standard C Library (libc, -lc) ## SYNOPSIS **#include \** ``` 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)](/sigaction/2.md). 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. 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(2)](/sigblock/2.md) or [sigsetmask(2)](/sigsetmask/2.md) 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 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(2)](/sigblock/2.md) or [sigsetmask(2)](/sigsetmask/2.md) call is made). This mask is formed by taking the current signal mask, adding the signal to be delivered, and *or*'ing in 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 a handler routine and mask to be used when delivering the specified signal. Further, 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)](/sigaltstack/2.md). If *ovec* is non-zero, the previous handling information for the signal is returned to the user. 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)](/abort/3.md) | | SIGEMT | create core image | emulate instruction executed | | SIGFPE | create core image | floating-point exception | | SIGKILL | terminate process | kill program | | SIGBUS | create core image | bus error | | SIGSEGV | create core image | segmentation violation | | SIGSYS | create core image | non-existent system call invoked | | 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 control terminal | | SIGTTOU | stop process | background write attempted to control terminal | | SIGIO | discard signal | I/O | | SIGXCPU | terminate process | cpu time limit exceeded (see | | SIGXFSZ | terminate process | file size limit exceeded (see | | SIGVTALRM | terminate process | virtual time alarm (see | | SIGPROF | terminate process | profiling timer alarm (see | | 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 | Once a signal handler is installed, it remains installed until another **sigvec**() call is made, or an [execve(2)](/execve/2.md) 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 above signal list for each signal's default action. If *sv\_handler* is SIG\_IGN current and pending instances of the signal are ignored and discarded. If a signal is caught during the system calls listed below, the call is normally restarted. The call can be forced to terminate prematurely with an EINTR error return by setting the SV\_INTERRUPT bit in *sv\_flags*. The affected system calls include [read(2)](/read/2.md), [write(2)](/write/2.md), [sendto(2)](/sendto/2.md), [recvfrom(2)](/recvfrom/2.md), [sendmsg(2)](/sendmsg/2.md) and [recvmsg(2)](/recvmsg/2.md) on a communications channel or a slow device (such as a terminal, but not a regular file) and during a [wait(2)](/wait/2.md) or [ioctl(2)](/ioctl/2.md). 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)](/fork/2.md) or [vfork(2)](/vfork/2.md) all signals, the signal mask, the signal stack, and the restart/interrupt 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 system calls continue to do so. ## NOTES The mask specified in *vec* is not allowed to block SIGKILL or SIGSTOP. This is done 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 The **sigvec()** function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ## 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/1.md), [kill(2)](/kill/2.md), [ptrace(2)](/ptrace/2.md), [sigaction(2)](/sigaction/2.md), [sigaltstack(2)](/sigaltstack/2.md), [sigblock(2)](/sigblock/2.md), [sigpause(2)](/sigpause/2.md), [sigprocmask(2)](/sigprocmask/2.md), [sigsetmask(2)](/sigsetmask/2.md), [sigsuspend(2)](/sigsuspend/2.md), [setjmp(3)](/setjmp/3.md), [siginterrupt(3)](/siginterrupt/3.md), [signal(3)](/signal/3.md), [sigsetops(3)](/sigsetops/3.md), [tty(4)](/tty/4.md) ## EXAMPLES On the VAX-11 The handler routine can be declared: ``` void handler(sig, code, scp) int sig, code; struct sigcontext *scp; ``` Here *sig* is the signal number, into which the hardware faults and traps are mapped as defined below. *Code* is a parameter that is either a constant as given below or, for compatibility mode faults, the code provided by the hardware (Compatibility mode faults are distinguished from the other SIGILL traps by having PSL\_CM set in the psl). *Scp* is a pointer to the *sigcontext* structure (defined in ⟨*signal.h*⟩), used to restore the context from before the signal. ## BUGS This manual page is still confusing.