.Bf -symbolic 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. 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) or sigsetmask(2) 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 signals 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) or sigsetmask(2) 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.
The sigvec function 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). 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
.In signal.h :