A/UX® Programmer's Reference Sections

sigaction(3P) sigaction(3P)
2
number.
The sigaction structure is defined in :
struct sigaction {
void (*sa handler) ();
sigset_t sa_mask;
int sa_flags;
} ;
If act is not NULL, it points to a structure specifying the action to
be taken when the signal is delivered. If oact is not NULL, the action
previously associated with the signal is stored in the location
pointed to by oact. If act is NULL, signal handling is unchanged.
When act is NULL, sigaction can be used to inquire about the
current handling of a given signal.
The sa_flags field of act can be used to modify the delivery of
a specific signal. If sig is SIGCHLD and the SA_NOCLDSTOP
flag is not set in sa flags, a SIGCHLD signal is generated for
the calling process if any of its child processes stop. If sig is
SIGCHLD and the SA_NOCLDSTOP flag is set in sa_flags, a
SIGCHLD signal is not generated for stopped child processes. If
the SA_ONSTACK bit is set in sa flags, the system delivers
the signal to the process on a sigDai stack specified by sigstack(2).
If the SA_INTERRUPT bit is set in sa flags, system
calls interrupted by a signal are not restarted. -
When a signal is caught by a signal-catching function, a new signal
mask is calculated and installed for the duration of the signalcatching
function or until sigprocmaskO or sigsuspendO is
called. This mask is formed by taking the union of the current signal
mask and the set associated with the action for the signal being
delivered, such as sa mask, and then including the signal being
delivered. If and when the user's signal handler returns normally,
the original signal mask is restored.
Once an action is installed for a specific signal, it remains installed
until another action is explicitly requested by another call to
sigaction or until one of the exec functions is called.
SIGKILL and SIGSTOP cannot be caught or ignored. The set of
signals specified by sa mask is not allowed to block these signals.
This is silently enfurced.
February, 1990
RevisionC